WO2005121650A1

WO2005121650A1 - An ‘installed’ air conditioning cooling capacity reduction run-around pre-cool / re-heat coil system

Info

Publication number: WO2005121650A1
Application number: PCT/GB2005/002181
Authority: WO
Inventors: Peter John Bayram
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-06-08
Filing date: 2005-06-02
Publication date: 2005-12-22
Anticipated expiration: 2006-12-08

Abstract

Maximum Summer refrigeration cooling capacity and energy consumption can be reduced for air conditioning systems that ordinarily require significant amounts of re-heating at Summer ambients (e.g. where 100% fresh air and high air change rates are specified for health and safety) by incorporating a run-around pre-cooling coil (1) that exchanges energy with multiple terminal run-around re-heat coils (3), or alternatively a single re-heat coil (see Fig. 5), located upstream of the conventional re-heater batteries (12). The cooling coil (2) and run-around pre-cool coil (1) may be combined into a single cooling coil (see Fig. 2) with an increased chilled water temperature differential, such that chillers may be operated in series for further cost and energy savings. At lower ambient temperatures supplementary conventional re-heating (12 & 13) is also required. The run-around and conventional re-heaters are operated in sequence to control room temperatures, or in the case of single re-heaters to control a constant supply air temperature.

Description

AN 'INSTALLED' AIR CONDITIONING COOLING CAPACITY REDUCTION RUN-AROUND PRE-COOL / RE-HEAT COIL SYSTEM

This invention relates to 100% fresh air supply air conditioning systems required to provide not only 'room' temperature and humidity control but also specific (and higher than normal) air change (a.c.) rates, as typically required for Pharmaceutical Laboratories. It also relates to positive (+ve) displacement ventilation cooling systems, dedicated outdoor air systems (DOAS), de-humidified fresh air supply systems (e.g.) to fan coil units and ventilation cooling systems; all supplying 100% fresh air at, or near neutral conditions.

Where a 100% fresh air supply is required to be cooled from Summer ambient conditions down to the dew point temperature of the required supply air condition (to obtain required room relative humidity), and where a specific relatively high room air change rate is required, it will be necessary to re-heat the chilled air to prevent 'room' over cooling. Such re-heat would normally be provided by an external energy source to multiple terminal branch duct mounted zone temperature control re-heater batteries.

Such dew point cooling and re-heat systems not only require very high specific values of refrigeration per sq. metre of space served, but also require high amounts of heating, even at maximum Summer ambient conditions.

According to the present invention there is provided a coil run-around heat recovery system within the 100% fresh air supply system comprising of a coil upstream of the main cooling coil and another coil, or multiple zone terminal coils downstream of the main cooling coil. The air that is chilled down to the required dew point by the main cooling coil cools fluid flowing in counterflow (to flow of air) through the downstream coil(s). This flow of cool fluid is supplied via pipework to be also counterflowed through the upstream coil, and thereby pre-cool the incoming 100% ambient Summer fresh air. The fluid flowing through the upstream coil is, in turn, warmed by the incoming hot fresh air and is pumped via pipework to the downstream coil(s) to re-heat the chilled air entering these coil(s) to the required 'room' supply air condition when ambient conditions are hot enough, and is otherwise further re-heated by supplementary re-heating coil(s). In this way at maximum Summer ambient conditions 'free' re-heat and 'free' pre-cooling is provided. At lower ambient conditions (to as low as those having the same dew point temperature as the supply air condition) some 'free' re-heat and pre-cooling is provided. The 'free' pre- cooling so generated at maximum ambient conditions significantly reduces the required capacity (and cost) of the refrigeration system. Also, of course, there are significant cooling and heating energy consumption cost savings.

The run-around pre-cool/re-heat coil system would normally operate continuously during the cooling cycle except where it may be considered economical to switch off the run- around system pump when the pre-cool/re-heat energy savings are less than the energy input to the pump.

Conventional ventilation systems generally supply high air change rates of fresh air to promote 'room' air movement. However, some reduction in temperature and de- humidification of the ambient supply air condition may also be desired. In such cases a run-around pre-cool/re-heat coil system can economically provide for cooling of the ventilation supply air, which in turn could mean that the supply air volume/air change rates can be reduced for further economic benefit. It can be shown that where multiple rooms/zones are served that a run-around system having multiple re-heat coils will be both more efficient and provide for a greater cooling capacity reduction (and cost saving) than a single coil re-heat system, especially where there may be differing air change rates and temperature requirements in the zones.

In the case of a primary fresh air supply to refrigeration (DX) fan coil units a run-around pre-cool/re-heat system would not only reduce the cooling load requirement for DX cooling of the primary fresh air, but also reduce the range of 'on' coil temperatures to the DX cooling coil. The effective range of 'on' coil temperatures could be further reduced by incorporating two (2), or more DX coil (and refrigeration system) stages arranged for 'row control' (e.g. a 2^nd stage of pre-cooling having 2 or 3 rows and a final stage having 4 or 6 rows). By incorporating a coil in the system exhaust air to the run-around system Winter pre-heating of the primary fresh air can also be provided for. To prevent possible cooling coil 'freeze-up' the DX systems could incorporate a hot gas by-pass, or other capacity unloading system. In addition supplementary re-heat could be provided by condenser water or hot gas from the 2^nd DX stage, then reverse cycle heat pump operation of the 1^st stage (with changeover to a downstream coil) similarly followed by reverse cycle operation of the 2nd stage (and changeover to outdoor air coil heat exchange). Smaller high 'room' air change, +ve displacement and DOAS systems could also utilise DX cooling (at much lower cost and with more efficiency than chilled water systems).

In the case of chilled water main coil systems such supplementary re-heat as is required could be provided by refrigeration condenser water. When less than maximum cooling is required the chiller units could also be sequentially changed over to heat pump operation to provide for further re-heat and Winter heating (with each chiller unit having separate pumps and fluid flow changeover valves).

For particularly high Summer ambient conditions pre-cooling can be further increased by incorporating into the run-around system a heat recovery coil in the exhaust air system which can, of course, also be used for Winter heating heat recovery (whether, or not required for additional pre-cooling). Fluid flow should by-pass the exhaust air coil when the temperature of the fluid from the pre-cool coil is cooler than the exhaust air temperature (during periods when 'free' re-heat is required). The pre-cooling effect of such an exhaust air coil can be enhanced by spray cooling the coil, or adiabatically pre- cooling the exhaust air, but would only be effectively useful where Summer ambient conditions are extremely high (the flow temperature of the fluid from the exhaust air coil should be high enough to enable re-heating). Where the exhaust air is corrosive there may still be an economic case for incorporating and routinely replacing an exhaust air heat recovery coil.

Spray cooling of the exhaust air coil, or adiabatic pre-cooling of the exhaust air should be particularly considered in the case of +ve displacement ventilation cooling systems and relatively high Summer ambient design conditions. Since the exhaust air temperature of +ve displacement ventilation cooling systems can be significantly higher (although of a correspondingly lower relative humidity) than 'room' conditions an exhaust air coil without spray cooling, or adiabatic pre-cooling is unlikely to be effective in increasing the pre- cooling effect of the run-around coil system.

A run-around pre-cool/re-heat coil system can also be applicable where some of the air is re-circulated, e.g. where air may be re-circulated from non-hazardous areas; such air should be introduced after the pre-cool coil and prior the main cooling coil. Similarly, where the air volume may be reduced during 'out-of-hours' significant energy savings are still likely as 'room' heat gains at such times will likely be significantly less, thus re-heat of the supply air may still be required. In the case of a single pre-cool coil/single re-heat coil system a heat pipe heat exchange system can possibly be used in lieu of a pumped fluid run-around system. Similarly, a thermo syphon system (with, or without a refrigerant pump) could also be used, but with the advantage that multiple coils can be accommodated. The inside surfaces of the coil evaporator tubes of such a thermo syphon system could be sintered to promote evaporation of refrigerant at reduced temperature differences.

In the case of a multiple coil re-heat system some of the re-heat can be provided by a supplementary main re-heat coil such that the size of the distribution pipework to the terminal coils can be reduced. Similariy, there can be more than one (1) pre-cool coil such that one (1) may act as a pre-heat/frost coil in Winter, or be an addition to an existing main cooling coil. Also similarly, where there may be several supply air systems each with run-around coils it would be possible for the respective pre-cool/re-heat coils to be connected in parallel into a single common pumped circuit.

A further variation would be to incorporate a run-around pre-cool/re-heat system into a multizone, or dual duct supply air system such that the re-heat coil would be located in the 'hot deck' and there would be a common main cooling coil, rather than a separate 'cold deck^* cooling coil.

Since the coils of a run-around coil system will require to be relatively deep the air pressure drop through the coils can be reduced when less than maximum duty is required through the use of motorised by-pass dampers (or face and by-pass dampers). Such dampers can be controlled in sequence with motorised fluid flow control valves, or even as the main means of control. Similarly, the capacity of the main cooling coil could be controlled by directly controlling the output of the fluid chiller(s). In any case the main cooling coil can be controlled to maintain a constant 'off coil' temperature, or via relative humidity sensor(s) located in the exhaust air or the 'room(s)'.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a simplified schematic representation of the basic components of a run- around pre-cool/re-heat system, together with the airflow and fluid flow arrangements.

Referring to the schematic drawing, the run-around coil system comprises a pre-cool coil 1 , a main cooling coil 2 and multiple terminal re-heat coils 3 (two (2), or more). The incoming hot Summer fresh air 4 is pre-cooled by the cool water 5 counterflowing through the upstream coil 1 which is supplied via pipework 6 from the re-heat coils 3. This fluid 5 is in turn warmed by the hot fresh air 4 as it counterflows through coil 1. This warmed fluid 7 is pumped via pipework 8 to the coils 3 to re-heat the air 9, and is cooled as it counterflows through the coils 3 by the air 9 that is at the dew point temperature that is necessary to obtain the required 'room' relative humidity. In order to prevent excessive re-heating (when ambient temperature 4 is high enough) fluid flow 7 through coils 3 is controlled by the motorised 3-port control valves 10. The pump 11 continuously circulates fluid through the run-around system as long as the control system is 'calling' for cooling. At some condition less than maximum Summer ambient (air temperature 4) the output of the multiple terminal re-heat coils 3 will require to be supplemented by re-heat coils 12, that would typically be supplied via flow & return heating pipework 13 and be controlled by 3-port motorised valves 10.

A variation is shown in Figure 2, wherein the pre-cool coil 1 and main cooling coil 2 (of

Figure 1) are, in effect, combined into a single main fluid cooling coil 14. With this system there will be a relatively large temperature differential between the fluid 5 flow temperature and the fluid 15 return temperature that would, therefore, suggest that the fluid chiller(s) 16 be operated in series (possibly also with a flow by-pass 17 in the case of particularly high temperature differentials between fluid temperatures 5 & 15). The fluid flow volume to the coil 14 should be such that the temperature of the fluid 7 will tend to approach the dry bulb temperature of the incoming hot fresh air 4, however the fluid 7 temperature is reduced as it passes through re-heat coils 3 prior to return to the chillers 16. Figure 3 shows, in schematic form, how alternatively a single chiller 16 can be utilised with a flow bypass line 17 to ensure that a minimum flow volume for the chiller is maintained, and would be regulated by valve 18. Shown in dotted line on Figure 3 is how two (2), or more, chillers 16 can be operated in parallel, or as a duty/standby arrangement.

A similar variation is shown on Figure 4 whereby coils 3 and 12 (of Figure 2) are in effect combined into a single deeper coil 3. Both the supplementary re-heat requirement and full Winter heating requirement being provided by a primary heat source 13 to heat exchanger 19. The control sequence for increasing re-heat/heating could be for a) first valves 10 modulate, b) when one (1) valve 10 becomes fully open the by-pass port of valve 20 would modulate and, c) when shut then pump 21 would operate and its speed modulated, all as dictated by whichever zone at any one time has the highest demand for heating. The by-pass port of valve 22 would modulate open as pre-heat is required (such that coil 14 becomes a pre-heat coil in Winter). Use of coil 14 and valve 20 not being applicable to a system retrofit, as there would be existing main heating coil(s). N.B. At higher than 'design' ambient conditions the by-pass port of the cooling coil control valve 23 can be opened (or other control strategies used) to maintain a minimum chiller flow volume and/or prevent chiller overloading (also applicable to other arrangements). A further variation is shown on Figures 5 & 6 whereby there is only a single main 'free' reheat coil 3 that could be applicable for use when a constant common supply air temperature is required, or a single space/main zone is served.

For clarity of illustration such details as standby chillers and pumpsets, out-of-service chiller by-pass lines and any other necessary isolating & regulating valves, etc. are not shown.

Claims

C L A I M S

1) A pre-cooling run-around coil that reduces the otherwise required 'installed' capacity of an air cooling coil that cools and dehumidifies a 100% fresh air supply down to 'dew point' and is subsequently re-heated by a run-around re-heat coil that is connected to the pre- cooling coil via a pumped closed loop pipework circuit that runs continuously, or virtually continuously during the cooling cycle, and when ambient conditions are insufficiently high to sustain adequate 'free' re-heat is additionally conventionally re-heated.

2) A coil run-around system, as claimed in Claim 1, wherein the air is less than 100% fresh air.

3) A coil run-around system, as claimed in Claims 1 and 2, wherein the re-heat coil is located in the 'hot deck' of a multizone, or a dual-duct supply air system.

4) A coil run-around system, as claimed in Claims 1 , 2 and 3, wherein it is a heat pipe system.

5) A coil run-around system, as claimed in Claims 1 , 2 & 3, wherein in lieu of a single run- around re-heat coil there are multiple zone control run-around re-heat coils, or a combination of a main re-heat coil and zone control run-around re-heat coil(s).

6) A coil run-around system, as claimed in any preceding Claim, wherein there are one (1), or more, pre-cooling coils.

7) A coil run-around system, as claimed in any preceding Claim, wherein a heat exchange coil(s) is(are) located in the exhaust air system(s) and incorporated into the run- around pipework loop.

8) A coil run-around system, as claimed in Claim 6, wherein the exhaust air heat exchange coil(s) may be evaporatively cooled in Summer, or the exhaust air is adiabatically pre-cooled.

9) A coil run-around system, as claimed in any preceding Claim, wherein there may be multiple 'main' cooling coils and multiple pre-cool/re-heat/exhaust air coils all connected via a common pumped closed loop pipework circuit.

10) A coil run-around system, as claimed in any preceding Claim, wherein the flow of fluid and/or air through the re-heat coil(s), or pre-cool coil(s) is controlled, as required.

11) A coil run-around system, as claimed in any preceding Claim, wherein the flow of air is by-passed, or partially by-passed around one (1) or more of the coils when required.

12) A coil run-around system, as claimed in any preceding Claim, wherein there is not necessarily a fluid circulating pump and wherein the pre-cool coil(s) evaporates fluid and the re-heat coil(s) condenses gas.

13) A coil run-around system, as claimed in Claim 12, wherein the internal surfaces of the evaporator coil tubes have a sintered surface specially designed to enable evaporation of refrigerant fluids at relatively small temperature differentials (between the evaporating fluid and the airflow).

14) A coil run-around system, as claimed in any preceding Claim, wherein the pre-cooling coil is combined with the main cooling coil (generally as schematically shown in Figures 2 & 3 with, or without multiple terminal re-heat coils) and incorporated into the chilled fluid pipework circuit.

15) A coil run-around system, as claimed in any preceding Claim, wherein one (1), or more of the refrigeration systems are water cooled so that condenser water can be used for supplementary re-heating, or DX refrigeration hot gas is used. 16) A coil run-around system, as claimed in Claim 15, wherein one (1), or more of the systems are reverse cycle heat pumps that may sequentially changeover to also provide for further supplementary re-heating through to Winter heating.

17) A coil run-around system, as claimed in Claim 16, wherein one (1) or more of the heat pump systems changes over to an outside air heat exchange configuration.

18) A coil run-around system, as claimed in any preceding Claim, wherein the air volume(s) may be variable. 19) A coil run-around system, as claimed in any preceding Claim, wherein there are no secondary conventional re-heat coil(s) and wherein the non 'free' re-heat heating requirements of the system are provided for via a heat exchanger that exchanges primary heat with the secondary heat of the run-around system, generally as shown in Figure 5. 20) A coil run-around system, as claimed in Claim 14 and any other subsequent and dependent claims, wherein the capacity of the main cooling coil is controlled by controlling the capacity of the chiller(s), i.e. there is no coil control valve.