Method for controlling the ventilation of an air-conditioning system

Abstract

A method and apparatus for supplying conditioned air to a room. The method utilizes a plurality of partial flows and the flows are controlled to assure a substantially constant impulse while accommodating varying heating or cooling demand in the room. This is accomplished by providing a primary flow from one outlet and a secondary flow from another outlet. The speed of the secondary flow is low compared to the primary flow so that variation in the secondary flow as to condition to accommodate to the heating or cooling demand in the room has no substantial effect upon the total impulse which is determined substantially by the constant primary air flow. The two outlets may be supplied from the same duct and may be positioned separately or adjoining one another. The secondary flow is preferably controlled by a thermostat which is connected to a throttling control device.

Description

This invention relates to an air-conditioning system of the kind being evident from the preamble in claim 1.

An air-conditioned room usually is supplied with a constant air amount, the temperature of which is adjusted to the heat or cooling demand of the room. Lately, however, also another type of air-conditioning system has come into use, viz. such at which the supplied air amount is varied in different parts of the installation with respect to the heat or cooling demand in said parts. The temperature of the supplied air, however, is the same in the different rooms supplied by the installation. Systems of this type, so-called VAV-systems (Variable Air Volume), can in certain cases render substantial advantages from an installation-technical aspect.

The supply of varying air amounts to a room involves, however, certain difficulties as at certain load cases a flow pattern in the room is to be established which is correct from a comfort-technical point of view. At known types of VAV-systems a decrease in the amount of supplied air results in a decrease of the throwing length of the air jet and in a deterioration of the co-ejection of room air. In order to overcome this problem, it was tried by complicated designs of the supply air devices or by pulsating the air jets to maintain an acceptable outflow speed also at low air flows. However, also at these improved systems considerable variations in the flow pattern are obtained. At supply air devices with pulsated air, moreover, one has to utilize special arrangements for the exhaust air system in order to collect the primary air, which is not supplied to the room.

The present invention has as its object to eliminate said disadvantages and produce a supply air system - of the type VAV-system at which at varying air flows the flow pattern can be maintained unchanged. This object is achieved according to the invention by the method defined in the attached claims 1-6.

The invention, thus, is based on the idea that, for maintaining a non-varying flow pattern, the impulse per time unit of the supplied primary air must be held constant at varying air flows. The theoretical background of the invention is explained as follows.

The supplied air amount per time unit being q.sub.m /n where q.sub.m is the maximum air flow at full load and n is a constant, the impulse per time unit is: ##EQU1## where v.sub.o is the outflow speed and A is the outflow area of the supply air device. The constant n, which expresses the ratio between the maximum air flow and the desired air flow, varies in the VAV-system mostly between 1 and 5, i.e. the smallest air flow is only 20% of the maximum air flow. At such small air flows (n=5), one finds the impulse per time unit of the air jet being only 1/25 of the value at full load (n=1). A variation of the impulse of the air jet of up to 25 times, of course, gives rise to greatly varying flow patterns in the room and is entirely unsatisfactory from a comfort point of view.

By dividing the supply air flow into two partial flows, each of which is supplied to the room through separate supply air devices with greatly varying outflow speeds, constant flow conditions can be obtained. The impulse per time unit for the total supply air flow can be expressed by

In that case, q.sub.1 may constitute the basic flow, which always is supplied, i.e. usually the magnitude 20% of the maximum total flow, and q.sub.2 may vary between 0 and an upper value, which consequently usually amounts to about 80% of the maximum total flow. By supplying the basic flow with a high speed and the varying flow with a very low speed, i.e. v.sub.1 >>v.sub.2, one finds that the impulse per time unit for the total supply air flow can be expressed by

At different supply air flows, therefore, a non-varying flow pattern in the room can be obtained.

The invention also relates to an apparatus for carrying out the method, which apparatus is defined in the attached claims 7-10.

The air-conditioning system according to the invention is described in greater detail in the following by way of some embodiments, with reference to the accompanying drawing, in which

FIG. 1 shows the supply air devices in detail when they are mounted at a wall in a room

FIG. 2 shows an embodiment of supply air devices mounted adjacent each other in a rectangular room, and

FIG. 3 shows an embodiment of supply air devices mounted spaced apart from each other in the same room.

It appears from FIG. 1 how the two partial flows to a room can be arranged when the supply air devices are located at one of the walls in the room. The constant partial air flow q.sub.1 is supplied by means of the supply air device 1. This device comprises an inlet passage 3, followed by a contraction portion 4, and an outlet passage 5 with comparatively small outflow area. The entire device preferably is given a rectangular cross-section having its greatest extension in the horizontal direction, but of course also other designs can be imagined. The device is terminated by a screen 6 with low pressure drop and of conventional design. The variable air flow q.sub.2 is supplied to the room via the device 2, which comprises an inlet passage 7, a diffusor portion 8 and an outlet passage 9, the outlet area of which is chosen so great that the outflow speed of the air is low compared to the outflow speed in the device 1. Also the device 2 is terminated by a screen 10 of suitable design. For restricting the air flow through the device 2, a fixed throttling means 11 is placed in the inlet passage of the device. The flow through the device is adjusted by a damper 12 or the like, which is controlled by a damper motor 13. The setting of the damper means is adjusted in view of the heat or cooling demand of the room by the thermostat 14. The fixed throttling means and the flow adjusting damper may, of course, be disposed in another way than shown in FIG. 1. For practical reasons, the two supply air devices 1 and 2 preferably should be supplied normally from one and the same duct system. If, however, two duct systems with different pressure are available, the device 1 is to be connected to the system with the higher pressure.

The supply air devices 1 and 2 may be placed optionally, either on the ceiling or on a wall, depending on the design of the devices. The FIGS. 2 and 3 show two imaginable locations at wall mounting in a rectangular room. When the devices are placed relatively tightly adjacent one another near the ceiling, as shown in FIG. 2, a relatively large co-ejection of the primary air flow q.sub.2 is obtained before this air flow could mix itself with the room air. With this arrangement of the supply air devices the devices, of course, can be assembled to form a single combined device.

When the devices are placed apart, as in FIG. 3, for example one device near the ceiling and the other device near the floor, a relatively good admixture of room air will take place before the primary air flow q.sub.2 is co-ejected. The choice of the place for the supply air devices is determined a.o. by the temperature of the supplied air and by the way in which the room is utilized and shaped. The device 1 being located in the ceiling, the outflow passage 5 of the device should be formed so as to effect a horizontal outflow direction of the air.

The invention, of course, is not restricted to the embodiments shown in the drawing, but may be varied in the widest sense of the term within the scope of the idea on which this invention is based.

Claims

I claim:

1. In an air-conditioning system in which the ventilation in a space is varied upon demand without substantially changing the temperature or humidity of the air supplied to the space by varying the volume of conditioned air, the method of ventilating the space which consists of supplying the air to the space in a plurality of partial flows and maintaining the total impulse of the supplied air relatively constant independent of the volume of air supply between a minimum volume and a maximum volume, said method comprising the steps of maintaining at least one of said partial flows supplied to the space with a constant velocity and volume flow to thereby maintain the impulse of said one partial flow constant at a high impulse, and supplying at least one other of the partial flows at a velocity substantially below the velocity of said one partial flow to provide a low impulse, and controlling the ventilating by varying the volume of said low-velocity partial flow without substantially changing the temperature or humidity, said variation being between a minimum flow and a maximum flow, the impulse of the maximum flow in said other partial flow being substantially less than the impulse of said one constant partial flow so as to permit variation of the impulse of said other partial flow without substantially affecting the total impulse provided by the total of said partial flows, the impulse being determined by multiplying the velocity of the flow by the volume of the flow.

2. A method according to claim 1 wherein said partial flows are arranged in at least one pair including the high impulse flow and the low impulse flow.

3. A method according to claim 2 wherein said pair of flows are supplied to said space by a pair of inlets disposed in closely-spaced relation.

4. A method according to claim 2 wherein said high-impulse flow generates a circulation in the space into which the low-impulse flow is co-ejected along with space air.

5. A method according to claim 1 wherein said partial flows are taken from the same supply.

6. A method according to claim 1 wherein said high-impulse flow is taken from a high pressure supply and the low-impulse flow is taken from a low pressure supply.

7. A method according to claim 1 including the step of sensing the conditions within said space and controlling said low-impulse flow in accordance with the sensed conditions.