The cooling capacities of the greenhouses with the heat pump systems in Japan

David R. MEARS, Limi OKUSHIMA, Sadanori SASE,Tadashi TAKAKURA, Hideki MORIYAMA, Shinsuke FURUNO, Masahisa ISHII

Corresponding Author: L. Okushima, limi@affrc.go.jp

1 Introduction

Traditionally there has not been a significant cooling utilization of heat pumps, air conditioners or chillers for commercial greenhouse environmental control. A significant exception has been the use of refrigerant based air conditioning systems for cooling of relatively small greenhouse compartments used for biological containment where there is relatively high risk in quarantine facilities. Design principles for an integrated facility with sections providing various levels of biological containment including compartments that can be sealed and air conditioned for cooling without ventilation are described in Mears et al. (1997) and Mears and Kahn (1999). Containment during periods when cooling is required can also be an advantage when there is a need or desire for carbon dioxide enrichment and issues relating to the design of such a system are discussed in Albright and Henderson (1996).

Projects have been undertaken in The Netherlands to develop commercial greenhouse systems that are essentially closed throughout the year using the large aquifer underlying the commercial greenhouse production area as a massive thermal sink for seasonal energy storage for heating and cooling, Bot et al. (2005) and Opdam et al. (2005). Heat pumps are used to extract heat from a warm section of the aquifer in winter returning the cooled water to a cool section of the aquifer that will be utilized in water/air heat exchangers for warm weather cooling. The thickness of the aquifer in the region where these projects are implemented is on the order of 100 meters, providing a substantial thermal storage capacity. The possibility of implementing such a concept for Canadian conditions is discussed by Wong et al. (2007). They use a sophisticated finite element model to predict system performance under Canadian weather conditions. In Taiwan Fang (2009), has developed and implemented a unique application of heat pumps for orchid production. There are significant periods when both heating and cooling of adjacent growing areas are needed where one section needs a cool temperature to promote spike initiation while the other area requires higher temperatures for breeding stock. A heat pump cooling one water storage tank while warming another simultaneously provides appropriate heat sinks for both.

In Japan, with increasing fuel cost since 2008, many heat pumps have been installed for greenhouse heating. An advantage of heat pump systems is their use, not only for heating, but also cooling and dehumidification in greenhouses. Cooling and dehumidification by heat pumps has been introduced to greenhouse production for flowers such as roses and orchids, especially. Lilies in greenhouses with night cooling in Yamagata had longer stems and better quality (Furuno et al., 2012). Sunflowers, gerberas and cyclamens with mist cooling in daytime and heat pump cooling in nighttime demonstrated better qualities than those without cooling (Okazawa et al.., 2012). Some studies of greenhouses have shown that justification for the use of heat pumps requires high value crops in whole year production, because the installation cost of heat pumps are high. Semi Closed Management (SCM) systems have drawn some attention in Japan, too. The high CO2 applications in the 8 - 10 a.m. and 3 -5 p.m. periods in the greenhouse enhanced the yield and fruit quality of strawberry (Abe, et al., 2012). Meeting cooling requirements during these periods could be a significant factor to enable operation of SCM systems in Japan.

In this paper, the cooling performance simulation of three heat pump systems, which are: air source-air supply (A-A), water source-air supply (W-A), and water source-water supply (W-W) with a cool storage water tank, have been derived from the simple heat balance model developed by Both et al. (2005). The model and the conditions for the cooling calculations were similar to those used in the heating system calculations (Okushima, et al., 2012). The heating calculations showed that the heating performances varied widely depending on the design of system units, locations and set air temperatures. The water source heat pumps have advantages compared with the air source heat pumps because the water sources can generally draw heat from higher and more stable temperatures than outside air sources. The heat storage water tanks added to the water source heat pumps made the heating performances approximately 30 % higher than the water source heat pumps without the heat storage in the simulation results.

In the cooling mode calculations, 1) the cooling requirements for night cooling and full day cooling in four locations in Japan were estimated. 2) The sizes of the heat pumps for three systems were designed to satisfy the cooling requirements, and 3) the heat pump performance for the heating and cooling energy balance is discussed. 4) The hours for which ventilation would be required is also calculated for the three systems.

2 Methods

2.1 Simulation model The simulation model was based on steady state, one dimensional heat balance equations for each hour step in a year. The calculation consists of three parts, 1) cool demand calculation of the greenhouse, 2) running capacity calculation of the heat pumps and 3) for the W-W system, the cool storage and discharge calculation of the cool storage water tank and the heat exchangers. Those heat transfer equations are as follows:

(1)

(2)

(3)

(4)

(5)

!

Tstoret = Tstore

t"1 + Cstore "Cused _ store( ) Massstore " Lossstore # Tout "Tstoret"1( ) Massstore (6)

Notation:

Tin_set: Cool set air temperature inside the greenhouse (oC)

Tout: Outside air temperature (oC)

Rin: Solar radiation inside the greenhouse (W m-2)

HPsize: Heat pump size (kW)

Cneed: Total cool demand of the greenhouses (Wh m-2)

Hremoved_heatpump: Running capacity of the heat pump cooling (Wh m-2)

Cused: Cooling amount (Wh m-2)

Cused_heatpump: Cool supply from the heat pump (Wh m-2)

Cused_store: Heat removed from the cool storage (Wh m-2)

Cstore: Heat removed by the heat pump from the cool storage water tank (Wh m-2)

c1, c2 : constants of the heat pump cooling performance

EST: Entering water/air source temperature (oC)

ELT: Entering water/air load temperature (oC)

!T: EST - ELT (oC)

EWT: Entering water source temperature (oC)

Tstore: Water temperature of the heat storage water tank (oC)

cHEX: constant of the heat exchanger performance = 3164/floorarea (Wh h-1 oC-1 m-2)

NOHEX: the number of the heat exchangers

Massstore: Heat capacity of water in the heat storage water tank (W m-3 oC-1)

Lossstore: Total cool loss coefficient of the cool storage tank (W m-2 oC-1)

U: Total heat loss coefficient of the greenhouse (W m-2 oC-1)

super-script t: time step

The cool air was supplied to the inside of the greenhouses directly from the A-A and W-A heat pump systems. The results of night cooling and full day cooling with these three heat pump systems for greenhouses in Japan have been studied by the simulation. It was assumed that when the heat pump system could not supply the cooling requirement fully, the cooling with the heat pump system would be switched to air ventilation.

The W-W heat pump system had one cool storage water tank. The W-W heat pump produced cool water in the tank, rejecting heat to a geothermal sink as long as the cool storage is above a selected minimum temperature, 5oC for these studies. The heat exchangers use the cool water for greenhouse cooling if the cooling capacity is able to meet the total cooling requirement for the hour. If the heat exchanger and cool storage cannot meet the full requirement it is assumed the greenhouse will be ventilated for that hour. This control logic is a bit different than was the case for heating in (Okushima et al., 2012) where it was assumed a supplemental heating system would make up the difference between the capacity of the heat pump driven system and the full hourly requirement.

2.2 Parameters of the greenhouses The cooling performances of the heat pump systems were calculated in the case of the four types of greenhouses in Table 1.The set points of the inside air temperature was 30 oC in daytime and 20 oC in nighttime or 25 oC in daytime and 15 oC in nighttime for full day cooling, and 20 oC and 15 oC for night cooling at four locations, Abashiri, Yamagata, Tokyo and Kagoshima.

The models were calculated with the hourly weather data at the four locations. The weather data was derived from METPV-3 data during 1990-2003 by NEDO, http://www.nedo.go.jp/library/shiryou.html (2006). The ground water temperature for the water source heat pumps was 15 oC.

Table 1 shows the total heat loss coefficients for the 4 greenhouse types per m2 of floor area. These

conditions were the same as the heating calculation (Okushima, et al., 2012). In this study the structural heat loss and the capacities of the heat pumps, heat exchangers and storages are all modeled based on one unit of floor area, 1m2.

Table 1. Simulation cases Simulation case Case 1 Case 2 Case 3 Case 4 Structure type round super wide multi-span multi-span Floor area(m2) 300 600 1200 2000 Span No. 1 1 6 10 Width (m) 6 12 4 4 Length (m) 50 50 50 50 Eave height (m) 1.75 2.3 3.5 3.5 Ridge height (m) 2.78 5.8 4.9 4.9 Covering PO film PO film PO film PO film Area ratio of roof/floor

1.22 1.16 1.22 1.22

U (gable wall) (W oC-1 m-2)

4.0 4.0 4.0 4.0

U (side wall) (W oC-1

m-2) 4.0 4. 4.0 (day) / 3.0 (night

with thermal curtain) 4.0 (day) / 3.0 (night with thermal curtain)

U (roof) (W oC-1 m-2) 4.0 4. 4.0 (day) / 3.0 (night with thermal curtain)

4.0 (day) / 3.0 (night with thermal curtain)

Total U (W oC-1 m-2of floor)

7.58

6.82

(day) / (night) 6.72/5.20

(day) / (night) 6.25/4.86

2.3 The heat Pump performances The cooling performances of the heat pumps were modeled with the linear regression of cool capacity (CC) and entering temperature difference (!T).

The operating parameters shown in Table 2 for the three heat pump types are derived from the performance specifications of specific commercial units. The model SFYP224A (Daikin Co.) was selected as an A-A heat pump, model FLHP062 (Florida Heat pump Co.) as a W-A, and GSW120 (ClimateMaster) as a W-W heat pump.

For each case equations are developed relating the heat transfer in the evaporator and condenser sides to the difference in entering fluid streams. To put these systems on a common basis, the coefficients in these equations are scaled so that a nominal 1 kW of cooling, will be delivered when both entering fluids are 16oC. Thus the equations indicate the differences between the types but for design of a specific system the actual data from the proposed unit under consideration can be used.

The A-A heat pump cooling output is based on !T, the difference in temperature of the outside air dry bulb and the greenhouse cooling set point temperature which is the entering air stream to the evaporator. For the W-A unit the cooling output is determined by the difference in temperature of the geothermal type source and greenhouse cooling set point temperature. For the W-W system with storages, the cooling output is determined by the difference in temperature of the geothermal type source and the temperature in the cool storage tank.

Table 2. The heating and cooling capacities estimated from the specification data

HC, Heating capacity per 1kW of heat pump size

CC, Cooling capacity per 1kW of heat pump size

A-A heat pump

(SFYP224A, Daikin Co. ) HC=1.00-0.00173*!T CC=0.870-0.0115*!T

W-A heat pump

(FLHP062, Florida Heat pump Co.)

HC=1.00-0.0171*!T CC=0.870-0.00678*!T

W-W heat pump

(GSW120, ClimateMaster) HC=1.00-0.00499*!T CC=0.870-0.00835*!T

2.4 The cold water storage tank and the heat exchangers It is assumed that the cool water storage tank and the heat exchanger are used to cool the greenhouse inside air for the W-W heat pump system. The upper and lower water temperature limits of the water storage tank can be varied for system optimization but are set at a minimum of 5 oC for the cool tank. The initial water temperature in the storage at the first hour in the year is set at 10 oC in the cool storage. In this paper, it was assumed that the heat losses or gains of the storage tank with the environment could be negligible. The heat exchange to cool water in the storage from the greenhouse inside air is calculated based on the specifications of the Model GLW660 (Modine Co.), Low Temperature Greenhouse Heating Unit. The heat transfer per oC difference in entering fluid streams is 3164Wh h-1 oC-1 with 218 m3 min-1 airflow and 152 l min-1 water flow.

Heat exchanger capacity would not be limiting as this paper mainly focuses on the heat pump sizes that could be required for greenhouse cooling in Japan. In all simulation runs the number of heat exchange units was adjusted relative to the heat pump capacity as represented in Appendix A so that heat exchange capacity was not limiting. In the same manner, for any given W-W heat pump size, the cooling contribution increased with increasing water storage tank size as Appendix A shows. Large enough sizes of the water tanks were used for the calculations in this paper so that water tank capacity was not limiting.

3 Results and Discussions

3.1 The cooling demands/requirements The annual cooling loads at the four locations are shown in Table 3. The demands for full day cooling keeping less than 30 oC in daytime and 20 oC in nighttime was 336 kWh m-2 y-1 in the average of Cases 1-4 in Abashiri. It was close to the heating demands with 15 oC set air temperature, 353 kWh m-2 y-1 in average value of Case 1-4 in Abashiri, but at the other three locations the cooling demands of 30/20 oC set day/night temperatures for full day cooling were much larger than the heating demands, that was about double in Yamagata, 4 times in Tokyo and 9 times in Kagoshima. Night cooling demands were much less than full day cooling demands and also small compared with the heating demands except for the 15 oC set air temperature night cooling in Kagoshima.

The heating demands per unit floor area decreased as the floor area increased, because the larger units have less glazed area relative to the floor area. Similarly, the night cooling demands per unit floor area decreased as the floor area increased. On the other hand, the full day cooling loads per

unit floor area did not decrease significantly as the floor area increased. This is reasonable as incoming solar radiation is based on floor area and radiation is the dominant heat load in daytime.

Table 3. The greenhouse annual cooling demands (kWh m-2 y-1)

Location Full day cooling Night cooling Heating

Abashiri Set Day/Night cooling temperatures Set heating temperature

Floor

Area

30/20 oC 25/15 oC - /20 oC - /15 oC 15 oC

Case 1 300 m2 315min 406min 3max 19max 434max

Case 2 600 m2 337 423 3 17 385

Case 3 1200 m2 339 422 2 13 308

Case 4 2000 m2 354max 434max 2min 12min 284min

Average 336 421 3 15 353

Location Full day cooling Night cooling Heating

Yamagata Set Day/Night cooling temperatures Set heating temperature

Floor

Area

30/20 oC 25/15 oC - /20 oC - /15 oC 15 oC

Case 1 300 m2 425min 561 18max 64max 256max

Case 2 600 m2 439 565max 16 58 227

Case 3 1200 m2 439 551min 12 44 181

Case 4 2000 m2 448max 555 11min 41min 167min

Average 438 558 14 52 208

Location Full day cooling Night cooling Heating

Tokyo Set Day/Night cooling temperatures Set heating temperature

Floor

Area

30/20 oC 25/15 oC - /20 oC - /15 oC 15 oC

Case 1 300 m2 462min 632max 39max 102max 137max

Case 2 600 m2 475 632 35 92 122

Case 3 1200 m2 470 605 27 70 96

Case 4 2000 m2 479max 608min 25min 66min 89min

Average 472 619 32 83 111

Location Full day cooling Night cooling Heating

Kagoshima

Floor

Area Set Day/Night cooling temperatures Set heating temperature

30/20 oC 25/15 oC - /20 oC - /15 oC 15 oC

Case 1 300 m2 659 866max 63max 144max 91max

Case 2 600 m2 668max 856 57 130 82

Case 3 1200 m2 657min 817 43 99 64

Case 4 2000 m2 664 815min 40min 92min 59min

Average 662 839 51 116 74

3.2 Daily cooling patterns of the heat pump systems The calculations assumed that the heat pump had an on-off controller. Even if the heat pumps might have an inverter controller in actual situation, the W-A type and the A-A type could supply or remove the heat amount, which was a match for the heat pump capacities at maximum. Therefore, Figure 1 shows that the 193 kW (50 metric ton) heat pumps could not supply all the cooling demand in daytime on July 24th, which was the hottest day in a year in Kagoshima. The W-A type could remove enough heat to keep under 20 oC in the night. However, when the W-A type could not remove enough heat to keep less than 30 oC during daytime, then it stopped running during 7 a.m. to 5 p.m. and the windows were opened for ventilation. The W-W system could supply the cooling demand till 10 a.m. on those days because the cool storage and the heat exchangers could remove more heat than that the W-A heat pump could remove alone. The W-W system could keep less than 30 oC from 7 a.m. to 10 a.m and from 5 p.m. to 7 p.m. However the cool energy in the cool storage tank was used up by 7 p.m. and the windows were opened for ventilation after 8 p.m. in the night. If the control strategy were changed to anticipate night cooling by changing to ventilation earlier so some of the cool storage could be saved to supply the full night cooling. These partial cooling hours without ventilation might be useful for semi-closed management.

(a) W-A

(b) W-W with the cool storage tank Figure 1. The daily cooling on July 24 by the heat pumps (50 Metric Tons = 193 kW) in the 1200 m2 greenhouse in Kagoshima. The day and night set air temperatures were 30 and 20 oC. The W-W system included a water tank with 2.5 m height and 7.0 m diameter and 19 heat exchangers.

3.3 Contribution of the HP size to full day cooling Figure 2 shows the annual cooling capacities by the heat pumps in Case 4 (2000 m2) with the day and night set air temperatures 30 and 20 oC for full day cooling.

In four locations, the cooling capacities of the A-A and W-A systems were similar and if the heat pump could supply all cool demand, the heat pump size of the A-A type would be 1366, 1240, 1107 and 1423 kW in Abashiri, Yamagata, Tokyo and Kagoshima, respectively. The size of W-A type would be 1108, 1089, 966 and 1112 kW, respectively. Those of more than 1000 kW might be unrealistic sizes. The peak cooling requirements were similar as this requirement is fundamentally the maximum incoming solar radiation, which is similar at all these locations. The W-W heat pump sizes, which could supply the total cooling required, were about 374, 355, 314 and 400 kW in the 4 locations. The W-W heat pump size to cover total cooling demand was significantly smaller than the sizes of the A-A and W-A heat pumps, although the heat pump sizes to supply full cooling demands were still very large compared with the sizes to supply heating demands.

A whole year of full day closed greenhouse operation with heat pump systems, especially with A-A or W-A, are very difficult to justify because of the huge heat pump size needed in Japan. If the heat pump could supply 50 % of the total cooling required, the heat pump sizes of the A-A type and W-A would be about 600 kW and the W-W type would be about 100 kW for the 2000 m2 greenhouse.

(1) Abashiri

(2) Yamagata

(3) Tokyo

(4) Kagoshima

Figure 2. The annual heat removed by the heat pumps in Case 4 (2000 m2) with the day and night set air temperatures 30 and 20 oC for full day cooling. The W-W system included a 2.5 m high x 7.0 m diameter cool storage tank and 19 Modine heat exchangers.

3.4 HP sizes from a viewpoint of heating and cooling balance In interpreting the results for the different systems and locations for night cooling, where daytime cooling is by ventilation, it is interesting to look at this cooling that can be covered by a system sized to provide 90% of the total heating requirements as reported by Okushima, et al. (2012). In Table4-(1), all heat pump systems sized this way could cover 95-100 % of the 20 oC night cooling demands except in Kagoshima. In Kagoshima only the W-W system could cover 100 % of the 20 oC night cooling demands, but the A-A and W-A systems could cover 86 and 62 %. In Yamagata and Abashiri all heat pump systems could cover 97-100 % of the 15 oC night cooling demands too.

For full day cooling (Table4-(2)), the W-W system sized to provide 90% of the heating requirement could cover 56, 53, 44 and 42% of the 30/20 oC full day cooling requirement in Abashiri, Yamagata, Tokyo and Kagoshima, respectively. The A-A and W-A heat pumps similarly sized to provide 90% of the heating requirement could cover only less than 17% at the four locations. It is an interesting point that the cooling capacities of the 25/15 oC full day cooling were bigger than that of the 30/20 oC full day cooling, in Abashiri and Yamagata. The reason is the hours that do not need cooling with heat pump under the 30/20 oC set condition were less than the hours under the 25/15 oC set condition. The hours which were 25 oC more and 30 oC less in day time and 15 oC more and 20 oC less in night time increased the full day cooling capacities in Abashiri and Yamagata. In Abashiri the 84 kW W-W heat pump system could cover 68 % of the 25/15 oC full day cooling requirement. In Abashiri, growing crops in cooler conditions than in other three locations might have advantages for summer production with the W-W heat pump systems.

Table 4. The cooling supplied by heat pumps sized to provide 90% of the heating requirement for Case 3 (kWh m-2 year-1)

The W-W system included a cool storage tank and 12 Modine heat exchangers.

(1) Night cooling

Location Heat pump type and the nominal

size (kW) to provide 90% of the

heating requirement

Night cooling capacity

（kWh m-2 y-1） % of night cooling

requirement

set Day/Night cooling temperature - /20 oC - /15 oC - /20 oC - /15 oC

W-W, 36 kW 27 69 100 97

W-A, 59 kW 26 28 95 40

Tokyo

A-A, 78 kW 27 35 99 49

W-W, 56 kW 12 44 100 100

W-A, 104 kW 12 44 100 100

Yamagata

A-A, 101 kW 12 43 100 97

W-W, 84 kW 2 13 100 100

W-A, 118 kW 2 13 100 100

Abashiri

A-A, 185 kW 2 13 100 100

W-W, 31 kW 43 88 100 89

W-A, 50 kW 27 21 62 21

Kagoshima

A-A, 67 kW 37 33 86 33

(2) Full day cooling

Location Heat pump type and the nominal

kW size

Full day cooling capacity

（kWh m-2 y-1） % of full day cooling

requirement

set Day/Night cooling temperature 30/20 oC 25/15 oC 30/20 oC 25/15 oC

W-W, 36 kW 204 44

W-A, 59 kW 38 8

Tokyo

A-A, 78 kW 49 11

W-W, 56 kW 234 240 53 44

W-A, 104 kW 39 74 9 14

Yamagata

A-A, 101 kW 42 76 10 14

W-W, 84 kW 263 285 56 68

W-A, 118 kW 34 135 7 32

Abashiri

A-A, 185 kW 82 140 17 33

W-W, 31 kW 197 42

W-A, 50 kW 36 8

Kagoshima

A-A, 67 kW 53 11

3.5 Cooling hours and ventilated hours

3.5.1 Night cooling (Fig. 3)

The total hours for which the greenhouses needed any cooling to keep under 20 oC in night were 156, 842, 1249, and 1754 hours in a year in Abashiri, Yamagata, Tokyo and Kagoshima, respectively.

The W-W system with a 20 kW heat pump could keep the 1200 m2 greenhouse closed under 20 oC in most nights in a year in Tokyo and Kagoshima. The greenhouse with 20 kW A-A or W-A heat pump had to open the ventilation for about 500 and 1250 hours in night in a year in Tokyo and Kagoshima.

In Tokyo the A-A heat pump with a nominal size of 80 kW would be needed to keep under 20 oC in night. The W-A was 60 kW size to keep under 20 oC and the W-W was only about 20 kW size.

The total hours for which the greenhouses needed cooling for 15 oC night cooling were 730, 1555, 2067, and 2443 hours in Abashiri, Yamagata, Tokyo and Kagoshima, respectively.

In Tokyo an A-A heat pump with a nominal size of 120 kW would be needed to keep under 15 oC in night. The W-A was 100 kW size to keep under 15 oC. The W-W size needed was about 40 kW.

The nominal size needed for night cooling of the W-W was about 1/4 or 1/3 of the size of A-A or

W-A heat pump.

3.5.2 Full day cooling (Fig. 4)

The total hours in which the greenhouses needed any cooling to keep under 30 oC in day and under 20 oC in night were 2138, 3110, 3933, and 4900 hours in a year in Abashiri, Yamagata, Tokyo and Kagoshima, respectively. In Kagoshima more than half the hours in the year need cooling to keep under 30 oC in day and 20 oC in night. The total hours which the greenhouses needed any cooling to keep under 30 oC in the day would be 1982(=2138-156, 2268(=3110-842), 2684(=3933-1249), and 3146(=4900-1754) hours in a year in four locations, respectively

The W-W system with a 150 kW heat pump could keep the 1200 m2 greenhouse closed under 20 oC in most nights and under 30 oC in day time in a year in Tokyo and Kagoshima. The greenhouse with 150 kW A-A or W-A heat pump had to open the ventilation for about 1500 and 2000 hours in a year in Tokyo and Kagoshima respectively. Fig. 4 might suggest the heat pump size depending on the hours growers want to keep the greenhouse closed.

(1) Tokyo

(2) Yamagata

(3) Abashiri

(4) Kagoshima

Figure 3. Heat pump sizes vs ventilation hours in Case 3 (1200 m2) at the night cooling. (Left is 20 oC night cooling and Right is 15 oC night cooling)

The W-W system included 12 heat exchange units and the cool water storage sized to be filled up to the maximum cool storage capacity by the heat pump with 62-67 hours running.

(1) Tokyo (set temperatures: day/night 30/20 oC)

(2) Yamagata (Set temperatures: day/night 30/20(left) and 25/15(right) oC)

(3) Abashiri (Set temperatures: day/night 30/20(left) and 25/15(right) oC)

(4) Kagoshima (set temperatures: day/night 30/20 oC)

Figure 4. Heat pump sizes vs ventilation hours in Case 3 (1200 m2) at full day cooling.

W-W system included 12 heat exchange units and the cool water storage filled up the maximum cool capacity by the heat pump with 62-67 hours running.

Appendix A. Effect of number of heat exchanger units and size of water storage tank for cooling For any given heat pump size, the cooling contribution increased with increasing heat exchange capacity as Figure A1 shows. The increasing rate was smaller as the number of heat exchangers increased.

In the simulations to generate the data discussed in sections 3.2-3.5, enough heat exchanger units were used for the calculations such that heat exchanger capacity would not be limiting. The priority in this paper is mainly a focus on the heat pump sizes that could be required for greenhouse cooling in Japan. Running some cases with varying sizes of storage have shown diminishing gains in performance for increases beyond that for meeting the heating need, (Okushima et al., 2012). For any given heat pump size, the cooling contribution increased with increasing water storage tank size as Figure A2 shows. The increasing rate of cooling contribution also becomes smaller as the size of the water storage tank increases. Large enough water storage tanks were used for the calculations in this paper such that further increases in capacity would have negligible improvement in performance.

Figure A1. W-W heat pump sizes vs cooling capacities of Case 4 (2000 m2) in Kagoshima 30/20 oC full day cooling. The cool water storage tank was 2.5m deep and 7.0m diameter.

Figure A2. Number of heat exchange units (Modine heat exchangers) vs cooling capacities of Case 3 (1200 m2) in Kagoshima with 30/20 oC full day cooling with W-W systems. D is diameter of the cool water storage tank with 2.5 m deep. The W-W heat pump size was 84 kW. the cool water storage with D=9, 7, 5,3 and 1m could be filled up the maximum cool capacity by the heat pump with 97, 59, 30, 11 and 1 hours running, respectively.

Note

This research was promoted by No. 21058 of Research and development projects for application in promoting new policy of Agriculture Forestry and Fisheries. We thank Daikin Co. for providing the specifications data of Model SFYP224A. The study does not make the particular products discussed here recommendations. They were used for the calculations as model cases. References ____________________Model FLHP GT062 Specifications, FHP Manufacturing Co., Fort Lauderdale, FL.

____________________Model GLW660 Specifications, Modine Manufacturing Co., Racine, WI.

____________________Model GSW120 Specifications, ClimateMaster, LSB Industries, Inc. Oklahoma City, OK.

____________________Model SFYP224A Daikin ref <<I expressed our thanks to Daikin in “Note” section, because Daikin does not open the data publicly.>>

Abe, S., Sato, J., Toida, Y., Yamasaki, M, 2012, Effects of CO2 application in the morning and afternoon on growth, yield and fruit quality of ‘Sagahonoka’ strawberry, Horticultural Research (Japan) Vol. 11(Separate-2), 181.(In Japanese)

Albright, L.D. and H.I. Henderson. 1996. Air conditioning greenhouses to increase effectiveness of carbon dioxide enrichment. ASAE paper No. 964007. ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. 15 pp.

Bot, G., van de Braak, N., Challa, H., Hemming, S., Rieswijk, T.H., van Straten, G. and Verlodt, I. 2005. The solar greenhouse: state of the art in energy saving and sustainable energy supply. Acta Hort. (ISHS) 691:501-508

Both, A.J., E. Reiss, D.R. Mears, and W. Fang. 2005. Designing environmental control for greenhouses: Orchid production as example. Acta Horticulturae 691(2):807-813.

Fang, W. 2009. Use of heat pumps for energy-saving in protected cultivation. Symposium of controlled closed systems toward efficient bioproduction. Matsudo, Chiba, Japan.

Furuno, S., Sugawara, K., 2012, Heat pump characteristics and application to flower production, The application of water source heat pump systems in greenhouse horticulture, NIRE, p. 13-24. (In Japanese)

Mears, D.R. and R.P. Kahn. 1999. Concepts and new designs for quarantine greenhouses. Published in Kahn, R.P., S.B. Mathur et al. Exotic pest and pathogen exclusion: Containment facilities and safeguards for imported seeds, plants and biological control organisms. APS Press, St. Paul, MN, Chapter 11, p74-92.

Mears, D.R., T.O. Manning and R.P. Kahn. 1997. New concepts and designs for quarantine greenhouses. Paper No. 9724, Northeast Agricultural and Biological Engineering Conference, July 14-16, College Park, MD. (P-03232-08-97)

Okazawa, T., Tahata, Y., Shimaji, H., 2012, Effect of greenhouse cooling on the crops in summer, The application of water source heat pump systems in greenhouse horticulture, NIRE, p. 35-38. (In Japanese)

Opdam, J., Schoonderbeek, G., Heller, E., & De Gelder, A. (2005). Closed greenhouse: A starting point for sustainable entrepreneurship in horticulture. ISHS: Acta Horticulturae , 691, pp. 517-524.

Wong, W., L. McClung, D. McClenahan, A. Snijders and J. Thornton. (2007). The application of aquifer thermal energy storage in the Canadian greenhouse industry. GreenSys Conference, Quebec City, Canada, June 2007.