EP0040529A2

EP0040529A2 - Environmental control system

Info

Publication number: EP0040529A2
Application number: EP81302179A
Authority: EP
Inventors: Alan Michael Turbard; Peter Neville Foley
Original assignee: BorgWarner Ltd
Current assignee: BorgWarner Ltd
Priority date: 1980-05-19
Filing date: 1981-05-15
Publication date: 1981-11-25
Also published as: ES8204136A1; EP0040529B1; ATE11696T1; ES502268A0; EP0040529A3; DE3168741D1

Abstract

An environmental control system, preferably for a swimming pool hall, has four control modes, namely dry bulb airtemperature control, humidity control, controlled selection of fresh air intake in response to a comparison of enthalpies of the recirculated air and of the non-recirculated admitted air, and control of the condensing pressure of refrigerant in a heat pump system.

The air conditioning system comprises a heat pump system including a multi-stage switchable cooler (8); a multi-stage switchable heater (18); a hot water heat-exchanger (19); and a closed circuit "run around circuit" water system (7, 6, 16). The condenser (22) of the heat pump system usesthe pool water as its heat sink.

Description

The present invention relates to an environmental control system, in particular to a system for controlling the environment in a closed space through which conditioning air is circulated.
It is known to provide an air conditioning system for use in a room within a building, where the air is extracted from one part of the room and then, after suitable conditioning, returned to the room. _However, such systems rely solely on the use of heat pumps for the conditioning of the air and are therefore relatively simple to control but equally demanding of energy supply. It is an object of the present invention to provide an environmental control system in which the traditional heat pump system can be augmented by means to enable the input of energy to the system to be minimised.
Accordingly, the present invention provides an environmental control system to control the condition of a space including: air conditioning means; and means for delivering air to the space via the air conditioning means, characterised in that said delivery means comprises means for monitoring the enthalpies of air from said space and outside air and for selectively delivering whichever of the two has the higher enthalpy when heating of the air in said space is required.
With such a system, the enthalpy of the air leaving the recirculating conduit and entering the closed space is at an optimum for the purpose required (namely either cooling the closed space or warming the closed space), and consequently the energy transfer required in order to bring the air to its desired final conditions is reduced. Preferably the selection of the source of the air for the return circuit can be by way of controlled, variable incidence vanes.
Further, optional features of the invention are defined in the subsidiary claims.
In order that the present invention may more readily be understood, the following description is given, merely by way of example, with reference to the accompanying drawings in which:-

FIGURE 1 is a schematic view illustrating the air recirculation path and the various means for conditioning the inlet air to the desired conditions; and
FIGURE 2 is a diagrammatic sequence chart of the operation of the various conditioning means illustrated in Figure 1.

The environmental control system in accordance with the present invention, as illustrated in Figure 1, is designed as a control system for the air within a swimming pool hall 1.
A swimming pool hall represents just one application of the environmental control system of the present invention, and provides an advantageous heat store in the form of the mass of water in the pool.
Air is introduced to the pool hall by way of an inlet end 2 of the air recirculation conduit 3 and extracted via fan 9, passes through an outlet 4 to the various elements of the air conditioning means which are effective to ensure that the temperature and humidity of the air arriving at the inlet 2 at the downstream end of the recirculation conduit 3 are as desired.
The extracted air first passes through a filter 5 and then through a heat-exchanger 6 of a water "run around circuit" into which heat exchange cool water is separately pumped by way of a pump 7, so as to extract heat from the air as it leaves the filter 5.
On the main return limb of the recirculating air conduit 3, the air encounters a cooler 8 forming part of a heat pump system to be described in detail below.
From the cooler, the movement of the air is to a distribution region from which the air either leaves by way of an atmospheric vent 10, after passing through dampers 11, or passes on through a further damper 12 to recirculate to the pool hall.
Just downstream of damper 12 is a fresh air inlet 13 through which air may be admitted into the recirculation air conduit 3, under the control of a third damper vane 14.
From the distribution region, the air (which will usually be a mixture of partly recirculated air and partly ambient fresh air) passes through a further filter 15 and on to a second heat-exchanger 16 linked to the first-mentioned heat-exchanger 6 and the pump 7 to complete the simple "run around circuit" using water as the heat exchange medium.
Movement of the air from the second heat-exchanger 16 is fan-assisted by means of a second fan 17 as it embarks on its passage towards a condenser 18 of the heat pump system.
The air leaving the heat pump condenser 18 is passed through a third heat-exchanger 19, which may be heated by either low pressure hot water or steam from hot fluid circulation system 20. Finally, the air leaves the recirculation conduit at the inlet 2 to the pool hall.
The control of the conditions of the air entering the pool hall through inlet 2 is achieved by way of various sensors:-

(a) A temperature, sensor Tl at the inlet 2 measures the temperature of the inlet air to ensure that it is below a predetermined maximum value.
(b) The enthalpy of the recirculating air entering the mixing location (just leaving the first-mentioned fan 9) is measured by means of a first temperature/humidity sensor THl. A comparative assessment of the enthalpy of the incoming air from the ambient air inlet 13 is made by means of a second temperature/humidity sensor TH2. A suitable controller, not shown, serves to compare the enthalpy values determined by the sensors TH1 and TH2, for a purpose to be described later.
(c) A window sensor Wl, sensing the surface temperature of the glass of the pool hall windows, is effective in the humidity control mode to vary the set point of the humidity value to ensure that, as far as possible, the dew point of the air entering the pool hall through inlet 2; is less than the glass surface temperature, thereby avoiding the likelihood of condensation occurring on the windows.
(d) A further temperature/humidity sensor TH3 measures the temperature and the humidity of the air leaving the filter 5 at the outlet 4 from the pool hall, in order to monitor the attainment and maintenance of, on the one hand, the set point dry bulb temperature and, on the other hand, the set point humidity value of the system.
(e) A pressure sensor 2i serves to measure the pressure of the refrigerant in a condenser receiver 22 of the heat pump system, in order to ensure that the pressure in the condenser can be maintained at an optimum value by a restoring action to be described later.

The water "run around circuit" comprising the first and second heat- exchangers 6 and 16 and the pump 7 is brought into operation simply by energising the electric pump 7 upon the instructions of a control unit (not shown). This then serves to extract heat from the air leaving the filter 5 and to impart heat to the air leaving the filter 15 on. its way back to the pool hall inlet 2.
The heat pump system comprises not only the cooler 8 and the condenser 18, but also a four-stage single speed compressor 23, a desuperheater 24, and the condenser receiver 22. The heat pump system comprises two parallel circuits, the first involving direct return of the refrigerant from the-desuperheater 24, by way of a shut-off valve B in a first refrigerant line 25, directly to the condenser/receiver 22. The second circuit comprises both a second refrigerant line 26 to the heater 18 and a third refrigerant line 27 from the heater 18 back to the condenser/receiver 22, the second and third lines 26 and 27 being linked by multiple parallel paths through the heater.
The condenser 18 is a four-stage heater comprising a first stage 18a which is always in circuit between the second and third refrigerant lines 26 and 27 from the desuperheater 24 to the condenser receiver 22. Downstream of the first stage 18a is a one-way refrigerant flow control valve 28a.
The condenser 18 further comprises three additional parallel stages 18b, 18c, and 18dto which refrigerant is introduced by way of a common valve A and from which it is extracted by way of three branch lines connected to a refrigerant outlet manifold 27a in which a further one-way refrigerant flow control valve 28b is situated.
Clearly therefore, assuming the compressor is operating, when the valve A is closed only the first stage 18a of the heater is in operation whereas with the valve A open all four stages are in operation.
The cooler 8 is similarly a four stage parallel device, with individual control valve 29a, 29b, 29c and 29d to switch the respective parallel stages on line individually to select any number of operative stages from one stage to four stages. Each of these valves 29a to 29d is controlled by a common control unit which in turn governs the operation of the valves A and B.
The four throttle valves control the refrigerant feed to the evaporator and thus reduce the operating _'pressure. The type of valve fitted to this system is a thermostatic expansion valve. The component S is a crankcase pressure regulator - used to protect the compressor against too high suction pressures.
The compressor 23 is a four-stage reciprocating compressor with the stages switchable so that for each of the four stages of the cooler 8 there will be a respective stage of the compressor 23 on line. In this way, the speed of operation of the compressor motor can be maintained constant and the pumping rate carefully matched to the throughflow capacity of the variable switchable cooler 8.
The desuperheater 24 in the heat pump system comprises a straightforward heat-exchanger to desuperheat the refrigerant leaving the compressor. The heat rejected may be used to heat a limited quantity of hot water for use, for example, directly or indirectly for shower water purposes.
As indicated above, the three dampers 11, 12 and 14 are controlled so as to select the desired ratio of recirculated air. The dampers themselves are controlled by a control unit which may comprise a particular control loop of the main control unit of the heat pump system, and is responsive to the enthalpy values determined by means of the recirculated air enthalpy-sensing temperature/ humidity sensor THl and the fresh air enthalpy-sensing temperature/humidity sensor TH2.
When the pool air dry bulb temperature determined by temperature/humidity sensor TH3 is below the set point, the dampers are adjusted so that the air to be delivered to the pool hall is from whichever source, i.e. the outside or the upstream part of the recirculation, has air of the higher enthalpy, whereas when the dry bulb temperature of the air in the pool hall is above the set point, the dampers will select air from the one of the two sources having the lower enthalpy. The operation of the vanes of the damper 12 on the one hand and those of the dampers 11 and 14, on the other, is controlled in a modulated manner in response to the magnitude of the difference between the enthalpy values detected by sensors TH1 and TH2.
The heater comprising the hot fluid circuit 20 and the third heat-exchanger 19 includes a pump 30 and a boiler (not shown) providing the source of hot fluid. A three-way variable control valve 31 is operated in a modulated manner so as to select, as a proportion of the total flow rate of pumped fluid in the circuit 20, the amount of that fluid which passes directly from the pump 30 to the valve 31 by way of a recycle line 32, the rest of the pumped fluid coming from the boiler by way of a line 33. The valve 31 can be modulated between a fully opened position in which the recycle line 32 is effectively blanked off, and a fully closed position in which the supply line 33 from the boiler is fully closed.
The condenser receiver 22 in the heat pump system has a pool water circulation circuit 34 by way of a three-way modulatable control valve WRl. Water is pumped around the circuit 34 by means of the pump 35 such that it leaves the condenser receiver 22 and is then passed along a conduit 36 to a tee where one line 37 passes direct to the valve WRl and the other line 38 passes to the pool. Water is extracted from the pool by way of a further line 39, back to the valve WRl.
The valve WR1 is controlled in response to the condenser receiver pressure detected by the pressure sensor 21. The intention is that this pressure 21 should be at an optimum value and thus, when the pressure 21 rises above its set point, the valve opens. On the other hand, when the pressure detected by sensor 21 falls, the valve WRl closes. In this way a steady state condition can be attained in which the proportion of the water pumped through the circuit 34 which has come from the pool by way of line 39 can be controlled due to the modulating operation of the valve WRl. In this way, heat extracted from the air in the recirculating conduit 3 (by means of the cooler 8) can be dumped into the pool water. However, if the pool water temperature reaches its maximum design temperature, the heat pump system is controlled such that all stages of the cooler 8 are off and the compressor 23 is de-energised, to prevent further heat dumping, and so avoid too high an evaporation rate of the pool water which would create difficulties.
It is a particularly interesting and important feature of the embodiment that when the dry bulb temperature of the air in the pool hall initially falls below the set point temperature, the initial recovery action involves bringing on line the heater comprising hot fluid control circuit 20 with its heat-exchanger 19. This is instead of initially bringing the heat pump system on line.. This is because, when operating on only its first stage, the efficiency of the heat pump is at its lowest and to restore the temperature to the set point from a small undertemperature value, it is.more economical of prime energy to use the prime energy to heat the air directly rather than to use it to operate the heat pump.
The water "run around circuit" comprising the first and second heat- exchanger 6 and 16 is in operation whenever the dry bulb temperature of the pool hall is below the set point, as this provides a relatively cheap means of effecting a measure of heat transfer between the warm air leaving the pool hall and the relatively cooler air on its way to the pool hall.
Once the dry bulb temperature has fallen more than 1°C below the set point, the hot fluid circuit 2₀ is switched off line, and the heat pump system progressively brought on line one stage at a time. Only when the temperature continues to fall despite'all four stages of the heat pump system being on line does the hot fluid circuit 20 come back on line in order to prompt temperature recovery. This enables optimisation of the energy consumption for the dry bulb temperature controlling mode in that the heat pump system would work at low efficiency for very small temperature differences below the set point, at which time the boiler and the hot fluid circuit 30 provide a better means of temperature recovery whereas when, in the optimum efficiency regime of the heat pump system, all four stages of the heat pump have been brought on line without achieving recovery of the dry bulb temperature, the boiler and the hot fluid control circuit are operated as a supplementary means of temperature recovery.
The normal operating sequence of the control system is illustrated in Figure 2 and will now be described, by way of example. It is convenient to consider the four operating modes separately, although of course they do to a considerable extent interact and it is therefore a simplification of the system operation to consider a particular excursion of one of the parameters in isolation.

Dry Bulb Temperature Control Mode.;

Starting from the set point of 27°, when the temperature drops below that value the pump 7 of the water "run around circuit" is immediately energised to start operation. Also, the pump 30 of the low pressure hot water (LPHW) circuit 20 (previously referred to more generally as a "hot fluid circuit") is energised and the three-way valve 31 is initially set to its position in which the boiler line 33 is closed off and the return line 32 is open. At this time, the compressor 23 is de-energised but the valve A is closed and the valve B is open so that the heat pump system is standing by to come on line shortly with one stage of cooler 8 and a single stage 18a of condensor 18.
Once the temperature has fallen to a first threshold value, in this case 26.5°C, the valve 31 will have been modulated to its position in which the return line 32 is closed off and the boiler line 33 is fully open, but this will have been ineffective to restore rapidly the dry bulb temperature measured by the sensor TH3. At this point, the LPHW pump 30 is de-energised and the first stage of the cooler 8 is brought on line by opening of the valve 29a and energising of the compressor 23 with one compressor stage effective.
At a second threshold temperature, in this case 26.25°C, the conditions of the valves A and B reverse so that valve B closes and valve A opens to bring the last three stages.18b, 18c and 18d of the condensor 18 of the heat pump system on line simultaneously with no refrigerant returning directly from the desuperheater 24 to the condenser/receiver 22 (because the valve B is closed). However, at this point only one stage of the cooler 8 and one compressor stage are on line.
At a third threshold temperature (in this case 26°C) the second stage of the cooler 8 is brought on line by opening of the valve 29b, and simultaneously a second stage of the compressor 23 is effective.
If the temperature continues to fall to a fourth threshold temperature, in this case 25.25°C, the third stage of the cooler 8 is brought on line by opening of the valve 29c, and a third stage of the compressor 23 is brought on line.
If the temperature falls still further to a fifth threshold value, in this case 24.5°C, the fourth stage of the cooler is brought on line by opening of the valve 29d and the fourth stage of the compressor 23 is also brought on line. At the same time, the heater circuit pump 30 is energised, but again with the three-way valve 31 in its position closing off the boiler line 33 and leaving the return line 32 fully open.
If the temperature falls below the above-mentioned fifth threshold value, the valve 31 in the low pressure hot water circuit progressively modulates to its alternative extreme position where the return line 32 is closed and the boiler line 33 is fully open, by the time a sixth threshold temperature, in this case 24°C, is reached. With the low pressure hot water system fully operational, and the heat pump also fully on line, the dry bulb temperature measured by sensor TH3 should recover.
As the temperature recovers, the valve.31 progressively modulates back to its position in which the return line 32 is fully open and the boiler line 33 is fully closed by the time the temperature of 24.5.°C has been attained; the pump 30 remains in operation until the temperature has recovered to 25°C. At this point all four stages of the cooler 8 and of the compressor will still be in operation.
At 25.25°C the fourth stage of the heat pump system is brought off line by a closing valve 29d and bringing one of the four compressor stages off line. After a further 0.75°C, when the temperature recovers to 26°C, the third heat pump stage is brought off line by closing down another stage of the compressor (leaving only two compressor stages in operation) and by closing valve 29c.
As the temperature rises through a further 0.5°C to 26.5°C, both stages of the heat pump will remain in operation but at 26.5°C the second stage of the cooler will be brought off line by closing of valve 29b and equally the compressor will be shut down to only a single stage operating. Right throughout the dry bulb temperature recovery phase, the valve A will have remained open and the valve B will have remained shut. This configuration is retained until the temperature has recovered to the value of 26.5°C at which point, with the single remaining stage of the cooler 8 still in operation, the valves A and B reverse so that the three last stages 18b, 18c and 18d of the condenser 18 are closed off and a proportion of the refrigerant leaving the desuperheater 24 returns to the condenser receiver 22 by way of the line 25.
Only when the dry bulb temperature has recovered to the set point does the last stage of the heat pump system come off line (by closing of valve 29a and shutting off the compressor 23).
It may be preferable for the temperature decrements required to bring the first and second stages into operation to be smaller (say 0.5°C) than the decrements required to bring in the third and fourth stages (say, 1°C); this would ensure that with falling temperature, the number of stages of the compressor which were operating would increase more rapidly - this could be important as the coefficient of performance increases as more stages of the compressor are brought into operation.
The water "run around circuit" remains in operation and is not in fact shut off until the dry bulb temperature has exceeded the set point of 0.5°C.
When the.dry bulb temperature is 1° above the set point, the heat pump first stage is switched on (with the valves A and B still in the "A closed -B open" configuration) so that one stage of the cooler 8 and one stage 18a of the heater will be operating and the system dumping heat to the pool water. If the temperature rises above 28°C, the vanes 12 are closed slightly and the vanes 11 and 14 are opened slightly so as to increase the fresh air intake in an attempt to depress the dry bulb temperature or in any event to reduce the humidity levels. The fresh air dampers 11 and 14 will be fully open and the recirculating air damper l2 fully closed by the time the temperature is 28.5°C, with the heat pump first stage still in operation.
If, during the dry bulb temperature excursion, the pool water reaches its maximum design temperature, measured by thermally responsive means (not shown), the heat pump first stage will be switched off in order to prevent further heat from being dumped to the pool water by way of the condenser receiver 22 and the pool water circuit 34.

Humidity Control.

The humidity control facility is of course interlocked with the dry bulb control such that in the event of an increase in humidity, the following sequence will occur:

Initially the heat pump first stage will be brought on line by opening valve 29a, the valve A being shut and the valve B being open so as to ensure that the primary stage 18a only of the heater is on line.

Upon further increase, the valve A opens and the valve B closes so as to bring the remaining three stages 18b, 18c and 18d of the heater on line.
Upon further increase, the second stage of the cooler is brought on line by opening of valve 29b and at the same time bringing a second stage of the compressor 23 on line.
A further increase in humidity leads firstly to bringing of the third cooler stage on line, and then finally to bringing the fourth cooler stage on line. As the relative humidity falls, the control sequence is the reverse.
In the event of a dry bulb error signal and a humidity error signal to the heat pump occurring simultaneously, a selector module of the control unit will determine which of these signals is the higher and will energise the heat pump accordingly.
The window sensor Wl is used to reset the set point of the humidity controller automatically in response to a change in the glass surface temperature, so as to ensure that at all times the humidity detected by the temperature/humidity sensor-TH3 is such that the dew point of the air in the pool hall is just less than the glass surface temperature, thereby avoiding the formation of condensation on the windows.
Under extreme conditions when the heat pump is unable to control the dew point of the pool hall air to remain below the glass surface temperature, the window sensor will then open the dampers 11 and 14, with corresponding slight closing of the damper 12, in order to increase the fresh air intake and thereby, hopefully, to depress the dew point temperature.

Refrigerant Pressure Control.

As mentioned above, the maintenance of design operating efficiency of the heat pump system requires limiting of the refrigerant condensing pressure. This is achieved by way of the pressure sensor 21 which controls the three-way valve WRl of the pool water circuit in such a way that if condensing pressure in the condenser/receiver 22 rises above its set point the valve WRl modulates open to bring more of the water in the line 34 from the pool line 39, whereas a fall in pressure detected by the sensor 21 will modulate the valve WRl closed so as to reduce the amount of the water in line 34 coming from line 39 and to bring a higher proportion straight from the condenser/receiver by way of the line 37.
The pressure control is totally independent of both the dry bulb and humidity controllers, but of course will interact with those control modes by virtue of its effect of changing the origin of the pool water in the condenser/receiver 22.

Enthalpy Comparison Control.

As explained above, the enthalpy comparison controller simply uses the temperature/humidity sensors THl and TH2 to determine the best source of air, i.e. recirculated air or fresh air, in order to ensure that the minimum energy transfer, and hence the minimum energy consumption, is needed under any particular mode of operation. The comparison of enthalpy is a continuous function and overrides other considerations determining the settings of dampers 11, 12 and 14. It was indicated above, with reference to the dry bulb temperature controlling mode, that the dampers bring in more fresh air if the dry bulb temperature exceeds the set point. It is this aspect of the damper control which may be overridden by the enthalpy comparison control circuit.
The enthalpy comparison control is reverse- acting in that when the system is operating in the heating mode the sensors TH1 and TH2 will select the air mixture (recirculating air or fresh air or combination of the two) which has the highest enthalpy, whereas in the cooling mode the air mixture with the lowest enthalpy will be selected.

Claims

1. An environmental control system to control the condition of a space including: air conditioning means; and means for delivering air to the space via the air conditioning means, characterised in that said delivery means comprises means for monitoring the enthalpies of air from said space and outside air and for selectively delivering whichever of the two has the higher enthalpy when heating of the air in said space is required.

2. A system according to claim 1 and including an air recirculation conduit including an air introduction passage for admitting outside air, the monitoring and delivering means including first and second enthalpy sensors responsive respectively to the enthalpy of the recirculated air upstream of said air introduction passage and of non-recirculated air at said air introduction passage to provide a second signal and means operative to compare the monitored enthalpies and to vary the quantity of air admitted by way of said air introduction passage.

3. A system according to claim 1 or 2,wherein the monitoring and air delivery means comprises a control unit connected to control vanes which control the flow of outside and space air to the air conditioning means.

4. A system according to any one of the preceding claims, wherein the monitoring and delivery means is arranged to select for delivery to the space, when cooling of the space air is required, the air having the lower enthalpy.

5. A system according to any one of the preceding claims, wherein said air conditioning means includes a heat pump system comprising means for extracting heat from air leaving the conditioned space and means for imparting heat to air entering the conditioned space, a fresh air inlet between said heat extracting means and said heat-imparting means for optionally introducing non-recirculated air to the air returning to said conditioned space, a heat source separate from the heat pump for introducing heat to the air entering said conditioned space and a programmer for controlling said air conditioning means in response to the dry bulb temperature of air in said conditioned space, such that upon initial decrease of dry bulb temperature below a set point temperature the separate heat source is operated to heat the air entering the conditioned space, while the heat pump system is inoperative, and upon a greater marked drop of dry bulb temperature below said set point the heat pump system is brought on line to control the dry bulb temperature and the separate heat source is turned off.

6. A system according to claim 5, wherein said programmer is further effective to ensure that on an extreme difference between said set point temperature and an actual dry bulb air temperature below said set point the heat pump system is supplemented by the resumed operation of the separate heat source.

7. A system according to claim 5 or 6, and further including an additional heat transfer means between a heat-exchanger in the path of air just leaving _' said conditioned space and a heat-exchanger in the path of air entering said conditioned space and downstream of said fresh air inlet.

8. A system according to any one of claims 5 to 7, wherein said refrigeration circuit includes a variable capacity compressor whose on-line capacity can be increased as the heating demand increases.

9. A system according to any one of claims 5 to 8, wherein said fresh air inlet includes a variable air inlet facility and said programmer is effective to modulate said variable air inlet facility in response to attainment of a dry bulb air temperature in excess of said set point, whereby as the temperature difference between the set point dry bulb air temperature and a higher actual dry bulb air temperature increases, the proportion of air introduced at said fresh air inlet is increased.

10. A system according to any one of claims 5 to 9, wherein said conditioned space is a swimming pool hall and said refrigeration circuit includes a condenser having, as its heat sink,, a water circuit communicating with the water in said swimming pool.

11. A system according to claim 10, and including means responsive to the temperature of water in said swimming pool for de-energising the refrigeration circuit upon attainment of a desired maximum temperature for the pool water.

12. A system according to any one of claims 5 to 11, wherein said programmer includes a humidity control facility effective to control the operation of said heat pump system to maintain the humidity at a set point.

13. A system according to any one of claims 5 to 12, and including a control facility to said programmer, responsive to the window surface temperature and the humidity of said conditioned air, for controlling the admission of air through said fresh air inlet to increase the proportion of fresh air in order to reduce the humidity in the event of the heat pump, controlled by the above-mentioned humidity control facility, being incapable of bringing the dew point down below the window surface temperature.