U.S. patent application number 13/378035 was filed with the patent office on 2012-11-08 for district energy sharing system.
This patent application is currently assigned to DEC Design Mechanical Consultants Ltd.. Invention is credited to Erik Dean Lindquist, William Thomas Vaughan.
Application Number | 20120279681 13/378035 |
Document ID | / |
Family ID | 43355655 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120279681 |
Kind Code |
A1 |
Vaughan; William Thomas ; et
al. |
November 8, 2012 |
District Energy Sharing System
Abstract
A district energy sharing system (DESS) comprises a thermal
energy circuit which circulates and stores thermal energy in water,
at least one client building thermally coupled to the circuit and
which removes some thermal energy from the circuit ("thermal sink")
and/or deposits some thermal energy into the circuit ("thermal
source"), and at least one thermal server plant that can be
thermally coupled to external thermal sources and/or sinks (e.g. a
geothermal ground source) and whose function is to maintain thermal
balance within the DESS.
Inventors: |
Vaughan; William Thomas;
(West Vancouver, CA) ; Lindquist; Erik Dean;
(Sooke, CA) |
Assignee: |
DEC Design Mechanical Consultants
Ltd.
New Westminster
BC
|
Family ID: |
43355655 |
Appl. No.: |
13/378035 |
Filed: |
June 16, 2010 |
PCT Filed: |
June 16, 2010 |
PCT NO: |
PCT/CA2010/000969 |
371 Date: |
June 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61187626 |
Jun 16, 2009 |
|
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|
Current U.S.
Class: |
165/62 ;
165/104.13; 165/96 |
Current CPC
Class: |
Y02B 10/40 20130101;
Y02E 20/14 20130101; F24D 10/00 20130101; F24D 10/003 20130101;
F24D 11/0207 20130101; Y02B 30/12 20130101; Y02B 30/17 20180501;
F24D 2200/12 20130101; F25B 30/06 20130101; F24D 19/1039
20130101 |
Class at
Publication: |
165/62 ;
165/104.13; 165/96 |
International
Class: |
F25B 29/00 20060101
F25B029/00; F28F 27/00 20060101 F28F027/00; F28D 15/00 20060101
F28D015/00 |
Claims
1. A district energy sharing system comprising: a thermal energy
circuit comprising: a warm liquid conduit for flow of a heat
transfer liquid therethough at a first temperature; a cool liquid
conduit for flow of the heat transfer liquid therethrough at a
second temperature that is lower than the first temperature; and a
heat pump assembly comprising a reversible heat pump; a building
heat exchanger thermally coupled to the heat pump and for thermally
coupling to a client building; and a circuit heat exchanger
thermally coupling the heat pump to the thermal energy circuit;
piping fluidly coupling the circuit heat exchanger to the warm and
cool liquid conduits; at least one circulation pump coupled to the
piping; and a valve assembly comprising at least one control valve
coupled to the piping and switchable between a heating mode wherein
a fluid pathway is defined through the piping for flow of the heat
transfer liquid from the warm liquid conduit through the circuit
heat exchanger and to the cool liquid conduit, and a cooling mode
wherein a fluid pathway is defined through the piping for flow of
the heat transfer fluid from the cool liquid conduit through the
heat exchanger and to the warm liquid conduit.
2. A system as claimed in claim 1 wherein the valve assembly is
further switchable into an off mode wherein the warm and cool
liquid conduits are not in fluid communication with the heat
exchanger through the piping.
3. A system as claimed in claim 1 wherein the at least one control
valve is a modulating valve.
4. A system as claimed in claim 1 wherein the valve assembly
comprises a pair of three-way control valves wherein a first
three-way control valve is fluidly coupled to the warm liquid
conduit, cool liquid conduit, and an inlet of the circuit heat
exchanger, and a second three-way control valve is fluidly coupled
to the warm liquid conduit, cool liquid conduit, and an outlet of
the circuit heat exchanger, and wherein when the valve assembly is
in the heating mode the first three-way control valve is closed to
the cool liquid conduit and open to the warm liquid conduit and the
inlet of the circuit heat exchanger, and the second three-way
control valve is closed to the warm liquid conduit and open to the
cool water conduit and the outlet of the circuit heat
exchanger.
5. A system as claimed in claim 1 wherein the valve assembly
comprises a single four-way control valve having four ports and a
rotary actuator, the four ports comprising a first port fluidly
coupled to the warm liquid conduit, a second port fluidly coupled
to an inlet of the circuit heat exchanger, a third port fluidly
coupled to the cool liquid conduit, and a fourth port fluidly
coupled to an outlet of the circuit heat exchanger, and wherein the
rotary actuator fluidly couples the first and second ports and
fluidly couples the third and fourth ports in the heating mode, and
fluidly couples the first and fourth ports and fluidly couples the
second and third ports in the cooling mode.
6. A district energy sharing system comprising: a thermal energy
circuit comprising a warm water conduit for flow of water
therethough at a first temperature; a cool water conduit for flow
of the water therethrough at a second temperature that is lower
than the first temperature; and at least one circuit pump coupled
to at least one of the warm and cool water conduits for pumping the
water therethrough; a grey water injection assembly comprising a
grey water supply conduit fluidly coupled to the warm or cool water
conduit and for fluidly coupling to a grey water source such that
grey water is supplied to the warm or cool water conduit; and a
pressure control device fluidly coupled to the grey water supply
conduit or thermal energy circuit and operable to regulate water
pressure within the thermal energy circuit; a client building heat
transfer apparatus fluidly coupled to the warm and cool water
conduits and for thermally coupling to a client building such that
thermal energy can be transferred between the thermal energy
circuit and the client building; and a grey water take-off conduit
fluidly coupled to the warm water conduit and for fluidly coupling
to a client building such that grey water can be supplied to the
building for non-potable uses.
7. A system as claimed in claim 6 wherein the grey water injection
assembly further comprises a filtration device fluidly coupled to
the grey water supply conduit upstream of the pressure control
device.
8. A system as claimed in claim 6 wherein the pressure control
device comprises at least one pump operable to increase the
pressure of the grey water above the pressure of water in the
thermal energy circuit.
9. A system as claimed in claim 8 wherein the pressure control
device further comprises at least one control valve and a cushion
tank fluidly coupled to the pump and operable to vary the flow rate
of grey water to the warm water conduit.
10. A system as claimed in claim 6 further comprising a server
plant comprising: a circuit heat exchanger thermally coupled to the
thermal energy circuit and for thermally coupling to a heat source
or a heat sink or both; piping fluidly coupling the heat exchanger
to the warm and cool water conduits; and a pump coupled to the
piping, and wherein the grey water supply conduit is fluidly
coupled to the piping.
11. A system as claimed in claim 6 wherein the grey water has a
higher temperature than the water at the second temperature, and
the grey water supply conduit is fluidly coupled to the warm water
conduit.
12. A district energy sharing system comprising: a first and a
second thermal energy circuit each comprising a warm liquid conduit
for flow of a heat transfer liquid therethough at a first
temperature; a cool liquid conduit for flow of the heat transfer
liquid therethrough at a second temperature that is lower than the
first temperature; and a circuit pump coupled to at least one of
the warm and cool liquid conduits for pumping the heat transfer
liquid therethrough; and a thermal energy transfer station for
thermally coupling the first and second thermal energy circuits,
and comprising at least one of a: liquid transfer assembly fluidly
coupling the first and second thermal energy circuits and
comprising a pump operable to flow heat transfer fluid
therebetween; and a heat exchanger assembly thermally coupling and
fluidly separating the first and second thermal energy
circuits.
13. A system as claimed in claim 12 wherein the thermal energy
transfer station comprises only the liquid transfer assembly, which
further comprises: a warm liquid transfer conduit fluidly coupling
the warm liquid conduits of the first and second thermal energy
circuits; a cool liquid transfer conduit fluidly coupling the cool
liquid conduits of the first and second thermal energy circuits;
and a changeover assembly comprising piping fluidly coupled to the
warm or cool liquid transfer conduits and to the pump, and at least
one control valve fluidly coupled to the piping and operable in a
first mode which defines a fluid pathway through the piping from
the first thermal energy to the second thermal energy circuit, and
a second mode which defines a fluid pathway through the piping from
the second thermal energy circuit to the first thermal energy
circuit.
14. A system as claimed in claim 13 wherein the thermal energy
transfer station comprises only the heat exchanger assembly, which
comprises: a liquid-to-liquid heat exchanger having a first heat
transfer zone and a second heat transfer zone thermally coupled to
but fluidly separated from the first heat transfer zone; first
liquid transfer piping fluidly coupling the first heat transfer
zone to the warm and cool liquid conduits of the first thermal
energy circuit and second liquid transfer piping fluidly coupling
the second heat transfer zone to the warm and cool liquid conduits
of the second energy circuit; a pair of transfer pumps each
respectively fluidly coupled to the first and second liquid
transfer piping and operable to flow liquid from the first thermal
energy circuit through the first heat transfer zone, and to flow
liquid from the second thermal energy circuit through the second
heat transfer zone.
15. A system as claimed in claim 14 wherein the thermal energy
transfer station further comprises a pressure control device and
fluid conduit fluidly coupled to the first and second liquid
transfer conduits, and operable to the regulate the pressure
between the first and second thermal energy circuits, the pressure
control device comprising at least one of a pressure reducing
control valve and a booster pump.
16. A system as claimed in claim 14 wherein the thermal energy
transfer station further comprises at least one server plant, each
server plant comprising a heat pump assembly thermally coupling one
of the first or second liquid transfer conduits to at least one of
a heat source and a heat sink.
Description
FIELD OF INVENTION
[0001] This invention relates to a district energy sharing system
for sharing thermal energy between a server and a client in a
district.
BACKGROUND
[0002] Traditional building heating and cooling systems use primary
high grade energy sources such as electricity or fossil fuels to
provide space heating and/or cooling, and to heat or cool water
used in the building. The process of heating or cooling the
building spaces and water converts this high grade energy into low
grade waste heat with high entropy which leaves then the building
and is returned to the environment. For example, heated water from
showers or sinks will be discharged into the sewer, and thermal
energy in heated air will radiate and conduct through exterior
walls and into atmosphere.
[0003] Building heating and cooling systems consume major
quantities of non-renewable resources and contribute substantially
to global warming. Also, many industry processes discharge large
quantities of low grade thermal energy that causes further warming
of water courses and atmosphere.
[0004] Attempts have been made to utilize natural heat source and
heat sinks to provide efficient, environmentally friendlier
approaches to heating and cooling a building; for example, and as
shown in FIG. 1 (PRIOR ART), buildings in a district can each be
served individually by independent ground source heat pump systems.
This approach unfortunately, requires significant infrastructure
costs as each homeowner would need to install a heat pump system
with a geothermal ground loop.
[0005] A typical building district is shown schematically in FIG. 2
(PRIOR ART) and comprising client buildings each fluidly coupled to
a single-pipe warm water distribution circuit. In this schematic, a
heat source (e.g. a mechanical plant having a geothermal ground
loop) is thermally coupled to the circuit by a heat exchanger;
another heat exchanger is provided to thermally couple the circuit
to another fluid flow distribution circuit in an adjacent district.
Each building can be provided with a heat pump which is thermally
coupled to the circuit and which converts thermal energy from the
circuit into useful heat for domestic space or water heating. One
particular disadvantage with such a district is that each building
is serially connected to the circuit and thus the overall
efficiency of building heat pump operation is compromised as
downstream heat pumps will be working harder when all upstream heat
pumps are drawing heat from the circuit. Efficient operation is
also compromised when some building heat pumps are heating and some
are cooling, as there will be large temperature variances along the
circuit and additional measures will need to be employed to
maintain the temperature of the circuit within its design operating
range.
[0006] It would therefore be useful to provide an improved and
cost-effective system to heat and/or cool buildings which re-uses
at least some low grade waste heat produced as a result of domestic
space and water heating and cooling processes.
SUMMARY
[0007] According to one aspect of the invention, there is provided
district energy sharing system comprising a thermal energy circuit
and a heat pump assembly. The thermal energy circuit comprises: a
warm liquid conduit for flow of a heat transfer liquid therethough
at a first temperature; and a cool liquid conduit for flow of the
heat transfer liquid therethrough at a second temperature that is
lower than the first temperature. The heat pump assembly comprises:
a reversible heat pump; a building heat exchanger thermally coupled
to the heat pump and for thermally coupling to a client building; a
circuit heat exchanger thermally coupling the heat pump to the
thermal energy circuit; piping fluidly coupling the circuit heat
exchanger to the warm and cool liquid conduits; at least one
circulation pump coupled to the piping; and a valve assembly
comprising at least one control valve coupled to the piping and
switchable between a heating mode wherein a fluid pathway is
defined through the piping for flow of the heat transfer liquid
from the warm liquid conduit through the circuit heat exchanger and
to the cool liquid conduit, and a cooling mode wherein a fluid
pathway is defined through the piping for flow of the heat transfer
fluid from the cool liquid conduit through the heat exchanger and
to the warm liquid conduit. The valve assembly can be further
switchable into an off mode wherein the warm and cool liquid
conduits are not in fluid communication with the heat exchanger
through the piping.
[0008] The valve assembly can comprise a pair of three-way control
valves wherein a first three-way control valve is fluidly coupled
to the warm liquid conduit, cool liquid conduit, and an inlet of
the circuit heat exchanger, and a second three-way control valve is
fluidly coupled to the warm liquid conduit, cool liquid conduit,
and an outlet of the circuit heat exchanger. When the valve
assembly is in the heating mode the first three-way control valve
is closed to the cool liquid conduit and open to the warm liquid
conduit and the inlet of the circuit heat exchanger, and the second
three-way control valve is closed to the warm liquid conduit and
open to the cool water conduit and the outlet of the circuit heat
exchanger.
[0009] Alternatively, the valve assembly can comprise a single
four-way control valve having four ports and a rotary actuator. The
four ports comprise a first port fluidly coupled to the warm liquid
conduit, a second port fluidly coupled to an inlet of the circuit
heat exchanger, a third port fluidly coupled to the cool liquid
conduit, and a fourth port fluidly coupled to an outlet of the
circuit heat exchanger. The rotary actuator fluidly couples the
first and second ports and fluidly couples the third and fourth
ports in the heating mode, and fluidly couples the first and fourth
ports and fluidly couples the second and third ports in the cooling
mode.
[0010] According to another aspect of the invention, a district
energy sharing system comprising the thermal energy circuit and a
grey water injection assembly. The grey water injection assembly
comprises: a grey water supply conduit fluidly coupled to the warm
or cool water conduit and for fluidly coupling to a grey water
source such that grey water is supplied to the warm or cool water
conduit; a pressure control device fluidly coupled to the grey
water supply conduit or thermal energy circuit and operable to
regulate water pressure within the thermal energy circuit; a client
building heat transfer apparatus fluidly coupled to the warm and
cool water conduits and for thermally coupling to a client building
such that thermal energy can be transferred between the thermal
energy circuit and the client building; and a grey water take-off
conduit fluidly coupled to the warm water conduit and for fluidly
coupling to a client building such that grey water can be supplied
to the building for non-potable uses.
[0011] The grey water injection assembly can further comprise a
filtration device fluidly coupled to the grey water supply conduit
upstream of the pressure control device. The pressure control
device can comprise at least one pump operable to increase the
pressure of the grey water above the pressure of water in the
thermal energy circuit. The pressure control device can further
comprise at least one control valve and a cushion tank fluidly
coupled to the pump and operable to vary the flow rate of grey
water to the warm water conduit.
[0012] According to yet another aspect of the invention, district
energy sharing system comprises a first and second thermal energy
circuit, and a thermal energy transfer station for thermally
coupling the first and second thermal energy circuits. The first
and a second thermal energy circuit each comprisie: a warm liquid
conduit for flow of a heat transfer liquid therethough at a first
temperature; a cool liquid conduit for flow of the heat transfer
liquid therethrough at a second temperature that is lower than the
first temperature; and a circuit pump coupled to at least one of
the warm and cool liquid conduits for pumping the heat transfer
liquid therethrough. The thermal energy transfer station comprises
at least one of a: liquid transfer assembly fluidly coupling the
first and second thermal energy circuits and comprising a pump
operable to flow heat transfer fluid therebetween; and a heat
exchanger assembly thermally coupling and fluidly separating the
first and second thermal energy circuits.
[0013] In one aspect the thermal energy transfer station comprises
only the liquid transfer assembly, which further comprises: a warm
liquid transfer conduit fluidly coupling the warm liquid conduits
of the first and second thermal energy circuits; a cool liquid
transfer conduit fluidly coupling the cool liquid conduits of the
first and second thermal energy circuits; and a changeover assembly
comprising piping fluidly coupled to the warm or cool liquid
transfer conduits and to the pump, and at least one control valve
fluidly coupled to the piping and operable in a first mode which
defines a fluid pathway through the piping from the first thermal
energy to the second thermal energy circuit, and a second mode
which defines a fluid pathway through the piping from the second
thermal energy circuit to the first thermal energy circuit.
[0014] In another aspect, the thermal energy transfer station
comprises only the heat exchanger assembly, which further
comprises: a liquid-to-liquid heat exchanger having a first heat
transfer zone and a second heat transfer zone thermally coupled to
but fluidly separated from the first heat transfer zone; first
liquid transfer piping fluidly coupling the first heat transfer
zone to the warm and cool liquid conduits of the first thermal
energy circuit and second liquid transfer piping fluidly coupling
the second heat transfer zone to the warm and cool liquid conduits
of the second energy circuit; and a pair of transfer pumps each
respectively fluidly coupled to the first and second liquid
transfer piping and operable to flow liquid from the first thermal
energy circuit through the first heat transfer zone, and to flow
liquid from the second thermal energy circuit through the second
heat transfer zone.
[0015] The thermal energy transfer station can further comprise a
pressure control device and fluid conduit fluidly coupled to the
first and second liquid transfer conduits, which is operable to
regulate the pressure between the first and second thermal energy
circuits. The pressure control device in this case comprises at
least one of a pressure reducing control valve and a booster
pump.
[0016] The thermal energy transfer station can further comprise at
least one server plant. Each server plant comprises a heat pump
assembly thermally coupling one of the first or second liquid
transfer conduits to at least one of a heat source and a heat
sink.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a schematic of multiple buildings each
individually serviced by independent ground source heat pump
systems. (PRIOR ART)
[0018] FIG. 2 is a schematic of multiple buildings each fluidly
coupled to a single-pipe warm water supply circuit. (PRIOR ART)
[0019] FIG. 3 is a schematic of a district energy sharing system
according to one embodiment comprising a thermal energy circuit
having a warm water conduit and a cool water conduit, which are
both thermally coupled to multiple client buildings and to a
thermal server plant in a district.
[0020] FIG. 4 is a schematic of a district energy sharing system
according to another embodiment comprising the thermal energy
circuit thermally coupled to multiple client buildings and a
thermal server plant in a district, wherein heat transfer apparatus
in each building and in the server plant are illustrated.
[0021] FIGS. 5(a) to (i) are schematic illustrations of a heat pump
assembly in one client building, wherein FIGS. 5(a) to (c) show a
heat pump assembly according to one embodiment having a reversible
heat pump and a pair of three-way control valves configured to
operate in a heating mode (FIG. 5(a)), in a cooling mode (FIG.
5(b)), and in an off mode (FIG. 5(c)), and Figures (d) to (f) show
a heat pump assembly according to another embodiment having a
reversible heat pump and a single four-way control valve configured
to operate in a heating mode (FIG. 5(d)), in a cooling mode (FIG.
5(e)), and in an off mode (FIG. 5(f)), and FIGS. 5(g) to (i) shows
a heat pump assembly according to yet another embodiment having a
reversible heat pump and four two-way control valves.
[0022] FIG. 6 is a schematic of a district energy sharing system
according to another embodiment comprising a thermal server plant
thermally coupled to the thermal energy circuit, and a multiple
unit local heat transfer plant servicing multiple client buildings
in the district also thermally coupled to the thermal energy
circuit.
[0023] FIG. 7 is a schematic of a district energy sharing system
according to another embodiment comprising a thermal server plant
and multiple client buildings each having a heat transfer apparatus
and being directly thermally coupled to the warm and cool water
conduits of the thermal energy circuit.
[0024] FIG. 8 is a schematic of a district energy sharing system
according to yet another embodiment comprising a combined multiple
unit local heat transfer plant servicing multiple client buildings
in a district and thermal server plant.
[0025] FIGS. 9(a) to (h) are schematics of a district energy
sharing system according to yet other embodiments comprising a pair
of thermal energy circuits thermally coupled together by an thermal
energy transfer station wherein FIG. 9(a) shows each thermal energy
circuit thermally coupled to multiple client buildings and a
thermal server plant, FIG. 9(b) is a detail view of the transfer
station according to one embodiment for serving circuits having the
same pressure zone, FIG. 9(c) is a detail view of the transfer
station according to another embodiment for serving circuits having
different pressure zones, FIG. 9(d) is a detail view of the
transfer station according to yet another embodiment for serving
circuits having different pressure zones and having a pair of
thermal server plants, and FIGS. 9(e) to (h) show different modes
of operation for transfer of heat between circuits of the transfer
station shown in FIG. 9(b).
[0026] FIG. 10 is a photograph of a district with an illustration
of one embodiment of the district energy sharing system overlaid
onto the photographed district.
[0027] FIG. 11 is a schematic of a process of sharing thermal
energy within one embodiment of the district energy sharing
system.
[0028] FIG. 12 is a schematic of a district energy sharing system
having a grey water injection assembly according to yet another
embodiment.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0029] Referring to FIG. 3 and according to one embodiment, a
district energy sharing system (DESS) 10 comprises a thermal energy
circuit 12 which circulates and stores thermal energy in water, at
least one client building 20 thermally coupled to the circuit 12
and which removes some thermal energy from the circuit 12 ("thermal
sink") and/or deposits some thermal energy into the circuit 12
("thermal source") (note: the client buildings 20 shown in this
Figure are shown only drawing thermal energy from the circuit 12
and thus are all operating as heat sinks), and at least one thermal
server plant 21 that can be thermally coupled to external thermal
sources and/or sinks (e.g. a geothermal ground source) and whose
function is to maintain thermal balance within the DESS 10. The
DESS 10 can also include a network control and monitoring system to
regulate, measure, and optimize the transfer of thermal energy
during system operation (not shown).
[0030] The circuit 12 comprises a pair of water conduits 14, 16
respectively flowing water at different temperatures and which
serve to transfer and store thermal energy between the sources and
sinks (respectively, "warm" and "cool" conduits). A heat transfer
apparatus 30 in each building 20 fluidly interconnects the warm and
cool water conduits 14, 16 such that warm water can flow from the
warm water conduit 14 through the heat transfer apparatus 30 and
then into the cool water conduit 16, or vice versa. In the former
configuration, the heat transfer apparatus 30 operates to draw heat
from the warm water conduit 14 to heat the building 20 and then
deposits the cooled water into the cool water conduit 16; in the
latter configuration, the heat transfer apparatus 30 operates to
extract heat from the building 20 to cool the building 20 and
deposits that extracted heat into the warm water conduit 14.
[0031] The warm water conduit 14 and cool water conduit 16 are two
separate and parallel closed loops of piping which are fluidly
interconnected only at the client buildings 20 and server plant 21.
The piping system in this embodiment uses plain water as a heat
transfer liquid and the pipe is single wall uninsulated High
Density Polyethylene (HDPE). However, other liquids can be used as
a heat transfer liquid according to another embodiment, since the
circuit 12 is a closed fluid loop.
[0032] One or more circulation pumps 22 are fluidly coupled to the
piping and are operated to circulate water through the warm and
cool water conduits 14, 16. In particular, water is pumped through
the warm water conduit 14 at a first temperature ("warm water") and
cool water is pumped through the cool water conduit 16 at a second
temperature that is lower than the warm water temperature ("cool
water"). A suitable temperature range for the warm water is between
10 and 30.degree. C. and a suitable temperature range for the cool
water is between 5 and 20.degree. C. The two-pipe arrangement
provides an assurance that all client buildings 20 get the same
temperature water for the supply to the heat pumps.
[0033] While FIG. 3 is shown to have a pair of circulation pumps 22
each fluidly coupled to the warm and cool water conduits 14, 16,
these pumps can be replaced or supplemented by circulation pumps 24
in one or more client buildings 20 (client pumps), or in the server
plant 21 (server pumps) to circulate water throughout the circuit
12.
[0034] In normal use any client building 20 that has a net heating
load draws water off the warm water conduit 14 and returns it to
the cool water conduit 16, and any client building 20 in net
cooling mode draws water off the cool water conduit 16 and returns
it to the warm water conduit 14. Transfer of water from warm to
cool water conduits or cool to warm water conduits increases the
pressure of the receiving conduit, driving water back to the other
conduit through the thermal server plant 21, where heat is added or
removed. This transfer is achieved by natural means or by the use
of the circulation pumps 22, 24.
[0035] The thermal energy circuit 12 is designed to ensure that the
pressure difference between the warm and cool water conduits 14, 16
is always kept as low as possible to ensure that the client pumps
24 do not have to overcome a large head that could limit the flow
to the client and increase the pumping horsepower. This is achieved
by maintaining low velocities in the water conduits 14, 16 with
commensurate low friction loss and by normally maintaining the flow
in the warm and cool conduits 14, 16 in the same direction, so that
pressure drop from friction is similar in both conduits 14, 16
along the length of the circuit 12.
[0036] The thermal energy circuit 12 also acts as a thermal storage
device through oversizing the water conduits 14, 16 and varying the
temperature in the water conduits 14, 16 over time. A secondary
level of thermal storage can be provided by the soil surrounding
the conduit that ameliorates temperature change during high load
conditions. Oversizing the conduits 14, 16 also reduces friction
loss and pumping horsepower.
[0037] When heat is removed from the thermal energy circuit 12 to
heat one or more client buildings 20 in the district and heat
removed from one or more other buildings 20 in the district is
transferred to the thermal energy circuit 12, these client
buildings 20 in effect share the thermal energy in the thermal
energy circuit 12 in their heating and cooling processes which is
more energy efficient than having the client buildings 20
discharging heat into the environment as a result of independently
operated heating and cooling processes. While it may be possible
that the thermal energy in the thermal energy circuit 12 can be
maintained fairly constant by designing the DESS 10 so that the
client and heat source buildings 20 collectively remove and return
about the same amount of thermal energy, the thermal sever plant 21
is provided to ensure a thermal balance is maintained in the DESS
10. That is, a net amount of thermal energy removed from the
circuit 12 by the client buildings 20 is returned to the circuit 12
by the thermal server plant 21 by drawing thermal energy from a
coupled external thermal source 23; similarly, a net amount of
energy deposited into the circuit 12 by the client buildings 20 is
removed by the server plant 21 and stored in a coupled external
heat sink 23. The heat source or sink 23 for the server plant 21
can be a geo-exchange field, ground water, ocean, lake, sewer,
effluent, refrigeration plants, solar collectors, ice rinks, or
industrial processes. These alternatives for server plant types
include any source that can produce or absorb heat, and transfer
the heat to or from the warm and cool water conduits.
[0038] Selecting suitable server heat sources will depend at least
on part on the temperature and capacity profiles as well as the
form of the heat provided by the heat source. Some server heat
sources provide consistent capacity whereas others provide a
variable capacity based on weather conditions, time of year, time
of day and other conditions. Selection of server heat sources is
based on the ability to satisfy client load profiles, and computer
modelling of capacity profiles can be performed to design a system
that can operate satisfactorily under any anticipated load.
[0039] Selecting suitable server heat sinks will depend at least on
the ability of the heat sink to store thermal energy for short or
long terms. The ability to store energy is based on the mass and
specific heat of the storage medium as well as the rate of heat
loss or gain. A viable high capacity storage system can incorporate
phase change medium where the heat of fusion can be used to store
large amounts of energy in a relatively small space and without
large temperature change. Eutectics can be selected that will pass
through a phase change at a specific temperature.
[0040] Short-term storage would typically be for a few hours and
could be applied to diurnal variations. Long-term storage could be
applied to seasonal variations depending upon the ability of the
medium to hold the heat. Thermal degradation is of less concern for
short term than it is for long-term storage. Even if the storage
degrades, it can be viable if it is being charged by energy that
would otherwise be wasted.
[0041] Referring now to FIG. 4, the heat transfer apparatus 30 in
each building 20 can comprise one or more heat pump assemblies that
can be configured to transfer low-grade (low temperature) energy
from the warm water conduit 14 into higher-grade energy that can be
used to heat the building 20. One or more other heat pump
assemblies can be configured to provide cooling for the building 20
and reject the by-product heat to the cool water conduit 16. Yet
some other heat pump assemblies having a valve switching assembly
(as shown in FIG. 4 and as will be described in detail below) can
be selectively configured to provide heating or cooling to a
building 20 by drawing heat from the warm water conduit 14 or
rejecting heat into the cool water conduit 16.
[0042] Heat pump assemblies can be water-to-air or water-to-water.
Water-to-air heat pump assemblies have heat pumps that are
typically small units that serve single rooms and can be fed
directly by the DESS 10 or by a closed piping loop that interacts
with the DESS 10 through a circuit heat exchanger. The heat pumps
in the buildings 20 can be operated in heating and/or cooling mode
so that the heat transfer to the circuit 12 is the net difference
between the heating and cooling loads. The DESS 10 thus could
replace a boiler and a cooling tower traditionally present in some
buildings.
[0043] Each heat pump assembly comprises a pair of heat exchangers
(respectively "circuit heat exchanger" 32 and "building heat
exchanger" 33,) and a heat pump 34 thermally coupled to but fluidly
separated from both heat exchangers 32, 33. The circuit heat
exchanger 32 is in fluid communication with both the warm water
conduit 14 and the cool water conduit 16. More particularly, the
circuit heat exchanger 32 has an inlet in fluid communication with
the warm water conduit 14, and an outlet in fluid communication
with the cool water conduit 16 such that water flows from the warm
water conduit 14 through the heat exchanger 32 and then to the cool
water conduit 16. The heat pump 34 is arranged so that its
evaporator is in thermal communication with the circuit heat
exchanger 32 such that some thermal energy in the warm water
flowing through the heat exchanger 32 is absorbed by the working
fluid in the heat pump 34, thereby cooling the circuit water which
then flows into the cool water conduit 16. The heat pump 34 is also
arranged so that its condenser is in thermal communication with the
building heat exchanger 33 such that the thermal energy absorbed
from the circuit water is discharged into the building 20.
[0044] In the embodiment shown in FIG. 4, an ice rink 20(a)
requires cooling and thus serves as a heat source, and the
following buildings require heating and thus serve as heat sinks: a
residential home 20(b), a low-rise apartment building 20(c), and a
high-rise apartment building 20(d). The residential home 20(b)
requires space heating and is heated by radiant heating; a radiant
heating system 36 in each of these buildings 20(a), 20(b) is
thermally coupled to the building heat exchanger 33 of each
respective heat transfer apparatus 30 and to the space which
requires heating in each building 20(a), 20(b). The low-rise
apartment building 20(c) also requires space heating and is heated
by both a forced air system 40 and by a radiant heating system 42
both of which are thermally coupled to the building heat exchanger
33 in this apartment building 20(c); the forced air system 40 has a
water-to-air heat pump assembly which transfers heat from a radiant
hot water loop coupled to the building heat exchanger 33 to air
ducts in the building 20(c). The high-rise apartment building 20(d)
comprises a series of heat transfer apparatuses 30 to provide space
heating and domestic hot water heating to the building 20(d). The
heat transfer apparatuses 30 which provide space heating have
water-to-air heat pumps and building heat exchangers 33 which are
thermally coupled to air ducts in the building 20(d); the heat
transfer apparatus 30 which provides domestic hot water heating has
its building heat exchanger coupled to a domestic water supply in
the building 20(d).
[0045] The server plant 21 in the embodiment shown in FIG. 4 is a
pump house 44 which is thermally coupled to a geothermal ground
loop 23(a) and a sanitary sewer 23(b). The ground loop can act as a
heat source and sink and the sanitary sewer 23(b) can serve as a
heat source. The pump house 44 comprises a heat pump assembly 46
having a pair of heat exchangers and a heat pump thermally coupled
to but fluidly separated from both heat exchangers: a circuit heat
exchanger is fluidly coupled to the thermal energy circuit 12 and a
ground loop heat exchanger is fluidly coupled to a fluid loop which
extends into and out of the ground. More particularly, the circuit
heat exchanger has an inlet fluidly coupled to the cool water
conduit 16 and an outlet fluidly coupled to the warm water conduit
14. When the ground source is used as a heat source, geothermal
energy is absorbed by the fluid pumped through the ground loop;
this thermal energy is transferred to the water flowing from the
cool water conduit 16 through the circuit heat exchanger.
Additional thermal energy can be obtained from warm wastewater
discharged from the sanitary sewer 23(b); a sanitary sewer heat
transfer apparatus 48 comprises a heat exchanger which is thermally
coupled to the wastewater and which has an inlet fluidly coupled to
the cool water conduit 16 and an outlet fluidly coupled to warm
water conduit 14.
[0046] A programmable controller (not shown) can be programmed to
control operation of the heat pump in the heat pump assembly 46 so
that sufficient geothermal energy is transferred to thermal energy
circuit 12 to maintain the warm water within the desired warm water
temperature range.
[0047] Referring now to FIGS. 5(a) to (i) and according to another
embodiment, one or more client buildings 20 in the district can be
provided with a reversible heat pump assembly 50 that can either
draw heat from the circuit 12 or deposit heat into the circuit 12.
The heat pump assembly 50 comprises a reversible heat pump 52, a
circuit heat exchanger 56 thermally coupling the heat pump 50 to
the circuit 12, a building heat exchanger 58 thermally coupling the
heat pump 52 to the client building 20, and a valve assembly and
circulation pump 55 both fluidly coupled to the warm and cool
conduits 14, 16 by piping 54 and which can be configured to direct
either cool water from the cool water conduit 16 or warm water from
the warm water conduit 14 through the circuit heat exchanger 56.
The heat pump 52 is thermally coupled to but fluidly separated from
both the circuit heat exchanger 56 and building heat exchanger 58.
The heat pump assembly 50 can be operated in a heating mode in
which case the valve assembly is configured to direct water from
the warm water conduit 14 through the circuit heat exchanger 56 and
to then into the cooled water conduit 16, and to operate the heat
pump 52 to absorb heat from water flowing through the circuit heat
exchanger 56 and to discharge heat into the building heat exchanger
58 (which in this Figure is shown coupled to a forced air system of
the building, but can be coupled to any building heat distribution
system as is known in the art). Conversely, the heat transfer
apparatus 50 can be operated in a cooling mode in which case the
valve assembly is configured to direct cool water from the cool
water conduit 16 through the circuit heat exchanger 56 and into the
warm water conduit 14, and to operate the heat pump 52 to absorb
heat from the building heat exchanger 58 and to discharge this
absorbed heat into water flowing through the circuit heat exchanger
56.
[0048] FIGS. 5(a)-(c) illustrates one embodiment of the valve
assembly comprising a pair of three-way valves 60, 62. A first
three-way valve 60 is fluidly coupled by piping 54 to the warm
water conduit 14, cool water conduit 16 and the inlet of the
circuit heat exchanger 56; a second three-way valve 62 is fluidly
coupled to the warm water conduit 14, cool water conduit 16, and
the outlet of the circuit heat exchanger 56. When the heat transfer
apparatus 50 is set in the heating mode as shown in FIG. 5(a), the
first three way control valve 60 is closed to the cool water
conduit 16 but open to the warm water conduit 14 and the inlet of
the circuit heat exchanger 54 and the second three-way control
valve 62 is closed to the warm water conduit 14 but open to the
cool water conduit 16 and the outlet of the circuit heat exchanger
54. As a result, a water pathway is provided through the piping 54
for water to flow from the warm water conduit 14, through the
circuit heat exchanger 56 and to the cool water conduit 16. When
the heat pump assembly 50 is set in the cooling mode as shown in
FIG. 5(b), the first three-way valve 60 is closed to the warm water
conduit 14 but open to the cool water conduit 16 and the inlet of
the circuit heat exchanger 54, and the second one-way valve 62 is
closed to the cool water conduit 16 but is open to the warm water
conduit 14 and the outlet of the circuit heat exchanger 54. As a
result, a water pathway is provided through the piping 54 for water
to flow from the cool water conduit 16, through the circuit heat
exchanger 56 and to the warm water conduit 16. The circulation pump
55 is coupled to the piping 54 at the inlet of the circuit heat
exchanger 56 and is operated to effect such flow.
[0049] The pair of three-way control valves 60, 62 can be solenoid
valves which are communicative with a controller programmed to
configure the control valves 60, 62 in their respective cooling
mode configuration and heating mode configuration. Alternatively
the pair of three way control valves 60, 62 can be manually
adjustable between their cooling and heating mode
configurations.
[0050] When the heat pump is off as shown in FIG. 5(c), both
control valves 60, 62 close one of their ports to stop flow of warm
water and hence flow of cold water through the piping 54.
Alternatively both valves 60, 62 close one of their ports to stop
the flow of cool water and hence flow of warm water. In either
position, water can still circulate through the piping 54 via the
remaining open ports.
[0051] The control valves 60, 62 can be a modulating valve which
can be modulated by a temperature sensor (not shown) in the supply
conduit to the heat pump 52 or a refrigerant pressure controller to
mix cool water discharged from the heat pump 52 with the warm water
from the warm water conduit 16 to maintain a maximum entering water
temperature or maximum refrigerant pressure.
[0052] Instead of a pair of three-way control valves, the same
functionality can be achieved by a single four-way control valve 63
as shown in FIGS. 5(d) to (f) and according to another embodiment.
The four-way control valve 63 has four ports A, B, C, and D and has
a rotary actuator that switches flow so that in one position it
connects port A to port B and port C to port D. When the valve
switches to its other position, it connect port A to port C and
port B to port D. Piping 54 is provided so that an inlet port of
the circuit heat exchanger 54 is coupled to port A, the warm water
conduit 14 is connected to port B, the cool water conduit 16 is
coupled to port C, and an outlet port of the circuit heat exchanger
54 is coupled to port D. In a first position of the control valve
63 warm water flows through the piping 54 and into the circuit heat
exchanger 54 and the cool water is discharged from the circuit heat
exchanger 54 into the cool water conduit 16. In the second position
of the control valve 63, cool water is directed into the circuit
heat exchanger 54 and warmed water is discharged to the warm water
conduit 16.
[0053] To stop flow through the heat pump, a two-way control valve
65 that closes when the heat pump is off is placed in either the
warm or cool supply pipes.
[0054] As can be seen in FIGS. 5(g) to (i), two pairs of two-way
control valves 64, 66 can be operated in a similar pair to the one
pair of three-way control valves 60, 62 to enable the heat transfer
apparatus to operate in both cooling and heating modes. In these
drawings, the control valves 64, 64 which are open are shown in
outline, and the control valves which are closed are shown in solid
black. As can be seen by the arrows in FIG. 5(g), a fluid pathway
through the piping 54 is defined by the opened and closed control
valves 64, 66 that warm water flows from the warm water conduit
through the circuit heat exchanger 56 and to the cool water conduit
16. Similarly, a fluid pathway is shown by the arrows in FIG. 5(h)
showing water from the cool water conduit 16 flowing through the
circuit heat exchanger 56 and to the warm water conduit 14. All
control valves 64, 66 are shown closed in FIG. 5(i) thereby
preventing flow through the piping 54.
[0055] Referring now to FIG. 6 and according to yet another
embodiment, the DESS 10 can be configured with one heat transfer
apparatus 30 servicing multiple client buildings 20 (hereinafter
referred to as a local heat transfer plant 70). The local heat
transfer plant 70 comprises a heat pump assembly 72 having a pair
of heat exchangers 74, 76 and a heat pump 78 thermally coupled to
these two heat exchangers 74, 76. One of these heat exchangers 74
is the circuit heat exchanger which fluidly interconnects the warm
and cool water conduits 14, 16 in the same manner as previously
described, i.e. with an inlet coupled to the warm water conduit 14
and an outlet coupled to the cool water conduit 16. The other heat
exchanger is the building heat exchanger 76 which is fluidly
coupled to a separate water circuit (hereinafter "building water
circuit" 80). The evaporator of the heat pump 78 is in thermal
communication with the circuit heat exchanger 76 and the condenser
of the heat pump 78 is in thermal communication with the building
heat exchanger 76 such that the heat pump 78 can be operated to
transfer heat from the thermal energy circuit 12 to the building
water circuit 80. Water in the building water circuit 80 is
circulated by pumps in the local heat transfer plant 70 to space
heating systems in each building 20(e), 20(f), 20(g), which can be
a fan coil air heating system as shown in building 20(e) or a
radiant heating system as shown in buildings 20(f), 20(g). A buffer
tank 84 is fluidly coupled to the building water circuit 80 to and
allows the heat pump to run long enough to avoid short cycling when
there is only a small load. The building water circuit 80 is also
fluidly coupled to a domestic hot water heat exchanger 86 which in
turn is thermally coupled to a domestic hot water circuit 88. The
domestic hot water circuit 88 includes a domestic hot water tank 90
and piping 91 which feeds heated water to each building 20(e),
20(f), 20(g) for domestic hot water use in those buildings. It can
be seen that thermal energy in the thermal energy circuit 12 is
transferred to the building water circuit 80 and then to the
building heating systems to provide space heating, and from the
building water circuit 80 to the domestic hot water circuit to
provided heated domestic water.
[0056] The thermal server plant in this embodiment is a
geo-exchange server plant 94 that is similar to the pump house 44
shown in FIG. 4 except that the geo-exchange server plant 94 is
thermally coupled to a ground source only.
[0057] Referring now to FIG. 7 and according to yet another
embodiment, the DESS 10 can be configured so that each building
20(h), 20(i), 20(j) in the district has its own heat transfer
apparatus 30, and the thermal server plant is the geo-exchange
plant 94 as shown and described for the FIG. 6 embodiment. The heat
transfer apparatuses 30 in each of these buildings 20(h), 20(i),
20(j) can be different types of space heating systems, such as a
water to air heat pump assembly in building 20(h) used in a forced
air heating system, and water-to-water heat pump assembly in
buildings 20(i) and 20(j) used in a radiant heating system.
Alternatively but not shown, the heat transfer apparatuses 30 can
also include one or more cooling systems (not shown) comprising a
circuit heat exchanger configured to absorb heat from a building
and discharge the absorbed heat into the thermal energy circuit 12.
Also alternatively, but not shown, the DESS 10 can include a local
heat transfer plant like the plant 70 in the FIG. 6 embodiment
which services other buildings in the district, such that some
buildings in the describe are collectively serviced by a local heat
transfer plant and some buildings have their own heat transfer
apparatus.
[0058] Referring now to FIG. 8, and according to yet another
embodiment, the local heat transfer plant 70 and geo-exchange
server plant 94 shown in FIG. 6 can be combined into a single
combined plant 100 which services multiple client buildings 20(k),
20(l), 20(m). These client buildings are each provided with a space
heating system 102 thermally coupled to the combined plant 100 and
with domestic hot water piping also thermally coupled to the
combined plant 100 in the same manner as described for the heat
transfer plant 70 in the FIG. 6 embodiment. In combining the heat
transfer plant 70 and thermal server plant 94, the heat pump
assembly 72 becomes thermally coupled to the heat pump plant water
loop instead of to the thermal energy circuit 12. The server plant
maintains its circuit heat exchanger which is in fluid
communication with the thermal energy circuit 12, and with the
server plant water loop. Thus, heat transferred from the thermal
energy circuit 12 to the server plant water loop via the heat
exchanger or from a ground source water loop via the ground heat
source heat transfer apparatus can be used to provide space heating
and domestic hot water to the buildings 20(k), 20(l), 20(m).
[0059] Referring to FIG. 9(a) and according to yet another
embodiment, a pair of DESS 10(a), 10(b) (first and second DESS A
and B) can be thermally and/or fluidly coupled together by a
thermal energy transfer station 110, embodiments of which are shown
in FIGS. 9(b) to (d).
[0060] The warm and cool water conduits 14, 16 in each circuit 12
(Loop A, and Loop B) are arranged so that the water travels in the
same direction in each conduit 14, 16 to maintain similar pressure
in each conduit 14, 16 at any point. The design is based on each
circuit 12 usually having one or more server plants 21 sized to
satisfy all the client buildings 20 in the circuit 12. However
server plant capacity and client building loads can vary from
minute to minute and season to season such that any one circuit 12
can end up with an imbalance that causes the warm and cool pipe
temperatures to drift above or below a set point. Conversely, to
achieve improved performance, an operator may want to change one
circuit's temperature in order to store energy for later use.
Another reason to transfer thermal energy from one circuit 12 to
another is the need to store surplus energy from one server plant
such as a wastewater treatment plant in a geo-exchange server that
can act a s a thermal battery.
[0061] When and if there is a thermal imbalance and thermal energy
needs to be transferred from one circuit 12(a) to another 12(b), or
through a series of circuits 12. To achieve this, a cross
connection between circuits 12 is provided by the thermal energy
transfer station 110 to transfer heat from one circuit 12 to the
other.
[0062] Three different embodiments of the energy transfer station
110 are described, as follows:
[0063] 1. Transfer of heat between circuits 12(a), (b) within the
same pressure zone (FIG. 9(b).
[0064] 2. Transfer of heat between circuits 12 (a), (b) of
different pressure zones (FIG. 9(c)).
[0065] 3. Transfer of heat between circuits 12 (a), (b) different
pressure zones and having at least one thermal server plant in the
transfer station 110 (FIG. 9(d)).
1. Transfer of Heat Between Loops in the Same Pressure Zone
[0066] Referring to FIGS. 9(b) and (e) to h), the transfer station
110 comprises a warm and cool water transfer conduit 120, 122
respectively coupling the warm and cool water conduits of the two
thermal energy circuits 12(a). A pump 124 is coupled to the warm
water transfer conduit 120 and can be operated to flow water from a
first circuit 12(a) to a second circuit 12 (b). The pump 124 has a
Variable Speed Drive (VSD) so the flow rate is adjustable.
[0067] A changeover assembly 125 comprising a pair of three-way
control valves 126 with associated piping and shut off valves
coupled to the warm water transfer conduit 120 allow the direction
of water flow to reverse. There are four modes of operation based
on the positions of the three way control valves 126 (open
positions of each valve 126 is shown in outline; the closed
position is shown in solid black). Mode 1 pumps water from the
first circuit 12(a) to the second circuit 12(b) (FIG. 9(e). Mode 2
pumps water from second circuit 12(b) to the first circuit 12(a)
(FIG. 9(f). Mode 3 allows free flow in either direction with the
pump off (FIG. 9(g) and Mode 4 allows no flow (FIG. 9(h). Mode 4
allows the circuits 12(a), (b) to operate independently with no
thermal energy transfer.
[0068] When transferring water through several circuits 12 (not
shown), it is possible to operate only one pump 124 in Mode 1 or 2
at one transfer station 110 and have the other transfer stations
110 in Mode 3.
[0069] A shut off control valve 128 is provided on the cool water
transfer conduit 122 to stop flow of water between the circuits
12(a), (b). The shut off control valve 128 is a secondary isolation
means that would close off in Mode 4 to ensure that there is no
flow through the cool water transfer conduit 122 due to pressure
differences between loops that are themselves cross-connected other
loops. The shut off control valve 128 is a modulating type that can
control the flow based on relative pressures in the two circuits
12(a), (b).
2. Transfer of Heat Between Different Pressure Zones
[0070] Referring to FIG. 9(c) and for circuits 12(a), (b) operating
at different pressures, the transfer station 110 transfers thermal
energy between circuits 12(a), (b) without transferring water. The
transfer station 110 comprises a liquid-to-liquid heat exchanger
112 with a first and second heat transfer zone that is thermally
coupled but fluidly isolated, and piping that fluidly couples the
warm and cool water conduits of each circuit 12(a), (b) with the
first and second heat transfer zones of the heat exchanger 112.
Transfer pumps 114, 116 are providing on the piping coupling each
circuit 12(a), (b) to the heat exchanger 112 and can be operated to
flow water from each circuit 12(a), (b) respectively through the
heat exchanger such that heat can be transferred in the heat
exchanger 112 from the warmer circuit to the cooler circuit.
[0071] The heat exchanger 112 is a stainless steel, cleanable
plate, counter-flow heat exchanger that are able to obtain an
approach of 1 Celsius degree. That is, one fluid exits the heat
exchanger 112 within 1 Celsius degree of the other fluid's entering
temperature. The transfer pumps 114, 116 pump the fluid from the
cool water conduit 16 to the warm water conduit 14 in each circuit
12(a), (b). This flow can be reversed so that the transfer pumps
114, 116 pump water from the warm water conduit 14 to the cool
water conduit 16 by using the changeover assembly for the pumps
used for scenario 1 (not shown).
[0072] Since pressure control of the system may be in one loop but
not the other, there is optionally a booster pump 118 and
associated piping for an increase in pressure, or a PRV if a
decrease in pressure is needed.
[0073] 3. Transfer of Heat Between Different Pressure Zones and a
Server in One Station
[0074] Referring to FIG. 9(d) a transfer station 110 similar to
that shown in FIG. 9(c) is provided additionally with a pair of
server plants 130 each coupled to the respective piping feeding
each side of the heat exchanger 112. This arrangement integrates
the heat exchanger 112 into the server plant building and can
simplify the pumping and control through the sharing of equipment
that provides heat transfer with equipment that is a source or
sink. Although each server plant is shown with an exemplary ground
source heat source and sink 131, the server plant 130 can be
thermally coupled to other heat source and sinks as described
above.
[0075] A typical arrangement would be one or more energy
source/sinks such as geo-exchange heat pumps connected directly to
a high pressure upper loop A and another set connected directly to
a low pressure lower loop B. Heat exchangers between the high
pressure and low pressure loops A, B with the capacity of one set
of heat pumps would allow all the heat pumps to serve either the
upper or lower loop. This arrangement would also allow the two
loops to operate independently or for heat to be transferred from
loop to loop without use of the heat pumps.
[0076] FIG. 10 shows a photograph of a district with the DESS 10
shown overlaid in illustration. The DESS 10 includes a waste water
heat recovery source 23, residential buildings 20 (client heat
sink), an ice arena 20 (client heat sink), and school, pool and
green house loads 20. The solid line indicates the warm and cool
water conduits of the thermal energy circuit. The dashed lines
indicate high temperature delivery conduits.
[0077] FIG. 11 is a block diagram which explains how energy can be
managed and balanced from multiple heat sources through the DESS
10, and how water can be recovered where available as a thermal
transport medium of the DESS 10.
[0078] According to another embodiment and referring to FIG. 12,
the DESS 10 includes a grey water injection assembly 150 for
flowing grey water from a grey water source 152 into the thermal
energy circuit 12 and transferring at least some of this water to
client buildings for certain domestic water uses.
[0079] The term "grey water" means non-potable water that does not
meet drinking water standards but can be used by a client building
for certain purposes such as toilet flushing, exterior washing or
irrigation.
[0080] In this embodiment, the thermal energy circuit 12, as well
as delivering thermal energy to client buildings 20, is capable of
providing grey water distribution to the client buildings 20. The
grey water can be used for toilet flushing and irrigation, thus
dramatically reducing the consumption of potable water. Although
the DESS 10 is normally a closed loop, the grey water injection
assembly 150 makes the DESS 10 partially open and therefore
requires that the piping in circuit 12 be suitable for an open
system using suitable materials such as plastic, non-ferrous metals
and stainless steel.
[0081] The grey water, which is clean effluent from a sewage
treatment plant, must meet certain standards to prevent build-up of
dirt or growth in the circuit 12 and especially in the heat
exchangers. There are also standards to be met for health reasons.
However the required standards are much lower than those for
potable water.
[0082] The injection of grey water does increase the flow of water
in the DESS but the grey water demand is much less than the water
flow required for the energy transfer. Therefore, the pipe size
usually does not need to be increased to accommodate the incoming
flow of grey water.
[0083] The components of the grey water injection apparatus 150 are
described:
[0084] A grey water supply conduit 153 fluidly couples the grey
water source 152 to piping in a thermal server plant 21; in this
case the grey water supply conduit 153 is coupled to a warm water
supply conduit 154 as the grey water is warm and can contribute
some thermal energy to the circuit 12; however, the grey water
supply conduit 153 can alternatively be coupled to a cool water
supply conduit 156 especially if the grey water is cool.
[0085] The grey water flowing the grey water supply conduit 153
first passes through a filtration device (not shown) to ensure it
meets required standards for health, particulate concentration and
biological growth potential. A pressure control device 156 is
coupled to the grey water supply conduit 153 downstream of the
filtration device and serves to regulate the water pressure within
the circuit 12. In particular, the pressure control device 156 has
a standard pressure boosting pumping system that increases the
pressure of the grey water to higher than the DESS 10. The pumping
system consists of an arrangement of pumps control valves and
cushion tank that delivers a variable flow of water to a set
pressure. The set pressure of the pumping system is the required
pressure for the DESS 10. The control device 156 can also include
one or more PRV to reduce water pressure in the circuit. The
pressure control device can further comprise at least one control
valve and a cushion tank fluidly coupled to the pump and operable
to vary the flow rate of grey water to the warm water conduit.
[0086] The warm supply conduit 14 feeding each client building 20
is sized to take both the heat pump flow and the simultaneous grey
water flow. For a typical house the DESS supply would be 1''
diameter and when the grey water is added it would be 1/4''
diameter. A buried take-off conduit 158 from the building's warm
supply conduit 159 would feed a water meter 160 to measure the grey
water use and then the water would connect to an irrigation system
and toilet flushing system (not shown) of the building 20.
[0087] Use of grey water by any client building 20 could reduce the
pressure in the entire circuit 12 and the pressure control device
156 would sense the pressure drop and introduce new grey water into
the DESS 10 to maintain the set pressure.
[0088] As noted above, the DESS 10 is a modular low grade thermal
energy network linking diverse heat sources and clients through a
low temperature, water-based piping system, and providing both
heating and cooling to buildings within the district. The DESS 10
is applicable to residential, institutional, commercial and
industrial districts. Any source of heat that can be transferred to
low temperature water can be integrated into the DESS 10 including
such diverse sources as geo-thermal, geo-exchange, ground water,
surface water, waste water, refrigeration systems, ice rinks, solar
collectors exhaust air streams, diesel generators, and chimneys.
The DESS 10 captures this low grade heat from these heat sources
and distributes it to clients that, by using heat pumps in heat
transfer apparatuses, convert the low grade thermal energy to a
higher grade for heating buildings and servicing water, or return
heat to the low grade system for air conditioning.
[0089] The thermal energy circuit 12 provides both an energy
delivery function as well as an energy storage function, and these
two functions enable sharing of thermal resources, and through
diversity, a reduction in required heat source size. The
temperature of the piping used in the thermal energy circuit 12 of
the DESS 10 is close to the ground temperature and therefore does
not need to be insulated. The piping can be high density
polyethylene (HDPE which is very low cost relative to other piping
systems and can be used because of the low operating
temperature.
[0090] Integrating conventional district energy solutions into
existing roads and buildings can be a logistical challenge that
frequently requires significant capital expenditures before
integration can be completed. Advantageously, the modular nature of
the DESS 10 and the relative ease of installing and tapping into
HDPE piping allow for gradual expansion and offer an early return
on capital expenditures.
[0091] The DESS 10 can be characterized by use of energy reserves
which are sources and/or sinks where energy can be drawn from or
stored for future use, such as ground, (static) aquifers, lakes,
and oceans. Other sources include those sources that have limited
storage capability, variable output range and must be reused in a
short period of time. These sources may include large energy
recovery sources where heating and cooling need to be drawn off to
be used in other areas, such as waste water effluent, air
conditioning, ice rinks, industrial processes, and co-generation
processes. Once the available sources are characterized, loads are
matched to the sources and multi-loop, hybrid systems developed for
combined residential, commercial and industrial applications
optimizing the efficiencies of the buildings connected to the DESS
10, minimizing the waste heat rejected to the environment, and
reducing peak loads by preconditioning the DESS 10.
[0092] The heat captured from the heat sources 23 can also be
stored, and storage options can be diverse, including ground
sources, thermal cistern storage, system infrastructure or pools.
The warm and cool water conduits 14, 16 offer a temperature
differential to significantly increase the efficiency of the heat
pumps used in the DESS 10. By pulling warm water from the warm
water conduit 14 for heating and returning the now much cooler
water to the cool water conduit 16 it becomes possible to offset
loads. Some systems are typically running in heating mode and some
in cooling; the DESS 10 offsets these loads which minimizes the
overall requirement for the district. Instead of the primary
sources like geo-exchange being the primary heat source or sink
they take on a greater role as a tool to balance the energy
requirements of the DESS 10 and as a large storage for seasonal
loads.
[0093] As shown in FIG. 12, the DESS 10 can also be used as a
conveyor of reclaimed water from a wastewater treatment plant or
other process wherein water is recovered. This increases the
efficiency of heat recovery from these sources and, subject to the
water quality meeting local health and environmental regulations,
the reclaimed water may be used to reduce demand for potable water
by using the reclaimed water for toilet flushing, irrigation,
stream augmentation and other water services not requiring potable
drinking water.
[0094] The DESS 10 can also be used as a vehicle to help manage
storm water by filtering it and, depending on its temperature,
routing it through the warm or cool water conduits 14, 16. In the
event of a major storm surge the DESS 10 may be able to help divert
excess storm water in one area of a community to another area in
the community that is better able to handle excess storm water. The
DESS 10 addresses the problems of comparable temperature systems,
and offers an efficient model for an expandable district system. It
utilizes a relatively low temperature warm and cool water conduits
14, 16 in the form of a loop as the primary distribution system.
Multiple loops of varying temperatures can be connected and
balanced to maximize the efficient transfer of energy from one loop
or network to another. In addition to developing large centralized
thermal energy systems, smaller localized thermal energy balance
transfer stations as shown in FIG. 9 ("mini-plants") can be used to
add new sources of thermal energy, and manage and balance thermal
energy among various loops and segments of loops. This latter
approach helps to match the capital costs of the DESS 10 with the
current phase of development or the tax base under consideration,
while allowing for a more scalable DESS 10 that can easily grow
with the development or expansion into an existing community. By
using small mini-plants at large sources and sinks it is possible
to capture low grade heat from the environment or equipment and
balance the warm and cool water conduits 14, 16. This approach also
allows for ease of expanding the DESS 10, and each of the plants
can divert energy to other parts of the DESS 10. The
interconnectivity increases the stability of the DESS 10 and allows
for easy expansion.
[0095] Mini-plants may contain any number of heat pumps, pumps,
heat exchangers and storage tanks to balance and control the
efficient collection, storage and transfer of thermal energy from
one loop to another. These mini-plants also help in preconditioning
the circuit 12 and also maximizing the efficient delivery of excess
thermal energy to storage locations throughout the circuit 12. The
storage locations may be storage tanks, which can be non
pressurized, plastic, fibreglass or metal and can be located inside
the mini-plant or buried outside. Multiple heat pumps allow the
plant to be expanded as the required capacity increases. The
mini-plants may be modular, factory built and tested and the
equipment can be housed in a concrete chamber, partly buried, or a
low height factory sheet metal enclosure with access panels similar
to rooftop equipment. In the case of larger buildings such as
multifamily residences or commercial buildings, the miniplants can
be incorporated into the buildings.
[0096] From an optimization standpoint, available energy sources
are evaluated on a site-by-site basis and the DESS 10 is designed
around the available sources to minimize the costs and maximize the
sustainability of the DESS 10. A DESS 10 can also be used to reduce
the overall energy required for a community's heating, cooling, and
domestic hot water, by balancing the energy required for heating
with the energy rejected from cooling, thereby reducing the overall
cost of the infrastructure. The heat rejected from buildings in one
area or gathered from one or more source or storage location can be
transferred to where heating is required. In this method the load
is shared across the district. Similarly, cool water rejected from
buildings in heating mode or gathered from one or more sources or
storage locations will be used to cool buildings more efficiently.
This sharing of heating and cooling energy reduces the overall
energy consumption in the network, and reduces the amount of
additional sources required.
[0097] A series of special components and sub assemblies can form
part of the DESS 10 and may include one or more of the following:
[0098] Low head high flow in-line pump arrangements. [0099] HDPE
venturi injection tees for source or client connections to impart
kinetic energy to the DESS mains water flow and allow one pipe or
two pipe operation.
[0100] One pipe operation allows one of the two pipes to be shut
down while the system still operates at the cost of lower
efficiency. [0101] Two or Four pipe building connection and valve
assembly to take advantage of one or two pipe DESS operation.
[0102] In-ground non pressurized stratified heat storage tanks with
water, or water and rock, in-fill. [0103] Mini-plants to connect to
a variety of loads, sources and the DESS and arranged to deliver,
withdraw, store energy and control the transfer of energy to and
from other mini plants and zones in the DESS network. [0104] Energy
metering device and software for flow, heating and cooling. [0105]
Software for network DESS flow and temperature control system.
[0106] Accessible, in-line, remote temperature and pressure
monitoring devices.
[0107] In North America the most available thermal energy sources
are typically low temperature sources, for which heat pumps are
required to boost the level of heating or cooling. Many heat pumps
are able to get a coefficient of performance over 5.5 when placed
in the DESS 10. This has the effect of reducing the overall
building energy consumption for heating and cooling by over 80%,
and the overall building energy consumption by over 45%. By
minimizing the overall electrical energy consumption in the
district, other alternative energies become more feasible, further
encouraging and increasing the sustainability of the project. When
considering the staging of distributed energy sources and
maintaining the flexible mechanical systems there are two options:
converting all energy sources to a common high temperature (may not
be feasible for smaller low grade energy sources) or distributing
at ambient temperatures. When retrofitting a neighbourhood, this
latter strategy can combined with mini-plant energy centres
containing heat pumps that can be used to boost the delivery
temperature up to 135.degree. F.-180.degree. F., depending on the
optimal integration requirements.
[0108] This strategy maximizes the efficiency of a low cost and low
energy loss ambient temperature distribution system with a high
temperature delivery system, that simplifies integration when space
in an existing mechanical room cannot be found. Because high
temperatures are only used for short distances, line losses can be
limited and energy delivered can be better managed, reducing the
overall life cycle costs of the DESS 10, while simplifying
integration requirements.
[0109] The thermal energy circuit 12 represents a potentially
significant thermal energy storage system, as a result excess
thermal energy can be stored in the circuit 12 by adjusting the
average temperature of one of the water conduits 14, 16 in the
circuit 12. This ability to store and adjust the water temperature,
or preconditioning of the water temperature, can have a number of
potential benefits, including peak shaving and load matching. Load
matching is done by monitoring both the outside air temperature and
building design temperatures and raising or lowering the circuit 12
temperature to better match the expected heating and/or cooling
loads, thus allowing the equipment to run more efficiently and
improve the performance of the heat pumps. Peak shaving is
accomplished by pre-conditioning the circuit 12 ahead to match
expected loads prior to reaching a threshold price for commercial
and/or residential electricity prices enabling the DESS 10 to
perform peak electricity shaving or peak shaving. By
pre-conditioning the circuit 12 ahead of peak energy costs for
electricity, fewer pumps and heat pumps need to run during these
hours and those that do run will run more efficiently. This will
reduce the peak load demand costs for buildings with demand load
charges and potentially significantly reduce the cost of
operation.
[0110] Although the circuit 12 represents a storage vessel for
thermal energy, additional storage can be added in terms of storage
tanks in the district or pre-heat tanks in the building. For
example, a preheat tank can be provided as part of the DESS 10.
[0111] Another key advantage of the DESS 10 is the use of modular
district energy. The DESS 10 provides infrastructure integration
which may integrate multiple sources (both sustainable and fossil
fuel based), manage overall energy demands and storage requirements
across an entire district; and is able to integrate multiple
communities and manage the demands and storage capabilities across
an entire "grid" or region. The distribution and delivery system
integrates low intensity/temperature distribution with high
temperature building connection requirements to minimize the cost
of retrofitting building systems; provides the benefits of
low/ambient temperature distribution with the needs of existing
building systems for higher temperature integration; and provides
building connections to meet the needs of existing building systems
for either low grade thermal energy or higher grade thermal
energy.
[0112] The DESS 10 provides reliability in that when mini-plants
are combined with a warm and cool pipe system in a "grid"
framework, individual mini plants can be taken off line for service
without compromising the DESS 10 as a whole. Interconnecting
modules within the DESS 10 cause improved reliability and
retrofitting costs are reduced by best matching the type of
building connections to the needs of the building. The DESS 10 can
use a plurality of pressure zones and thermal energy transfer
zones. Mini-plants provide ideal facilities to integrate different
pressure zones within a community or the DESS network. Adjacent
areas of the network have their own loops cross-connected with
transfer pumps and among two or more zones. To keep pressure in the
pipes to a reasonable level that allows for the use of lighter duty
pipes, where adjacent loops have substantially different
elevations, the cross connections may be by heat exchanger. As
discussed earlier, mini-plants also allow for the balancing,
management and transfer of energy from one zone to another, and can
be set up and controlled to route thermal energy across multiple
zones. Energy balancing can be provided given that alternative
energy sources have both daily and seasonal variations, making it
very difficult or cost prohibitive to build an entire district
energy system based on one source, alone. The modular nature of the
DESS and its ability to integrate multiple sources reduces the cost
of any given source by providing the overall energy demand of the
community is met; the energy provided is sustainable and these
sustainable sources can be used to increase density of potential
redevelopment.
[0113] Because high temperatures are only used for short distances,
line losses can be limited and energy delivered can be better
managed, reducing the overall life cycle costs of the DESS, while
simplifying integration requirements. To maximize the efficiency of
these higher output temperature heat pumps it may be necessary to
pre-condition the DESS circuit temperatures to provide a slightly
higher input temperature to these higher output temperature heat
pumps. This is particularly important when retrofitting a DESS into
an existing community where there are existing buildings with
specific heating constraints and a desire to reuse as much of the
existing building heating and cooling system as possible. This also
means that the overall loop temperature can be more dynamically
managed to reflect individual building heating and cooling
requirements, thus reducing energy supply costs and maximizing the
performance with which energy is transferred into each building on
the network. Loop temperatures can be more accurately controlled to
reflect the needs of the buildings for either heating and cooling.
In building equipment can be controlled to only pull what is
needed.
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