Energy Efficient Heat Pump System Applied Short Term and Seasonal Thermal Energy Storage Part 1 Design concept of the system

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1 Energy Efficient Heat Pump System Applied Short Term and Seasonal Thermal Energy Storage Part 1 Design concept of the system H. Wakayama NIHON SEKKEI,INC.KYUSYU BRANCH Fukuoka, Japan Tel: wakayama-h@nihonsekkei.co.jp S. Kindaichi University of Tokyo Tokyo, Japan K. Nagano Hokkaido University Sapporo, Japan T. Katsura Fujiwara Environmental Science Institute Ltd. Sapporo, Japan ABSTRACT This paper deals with the design concept of an energy efficient heat pump system installed in a hospital in Chiba prefecture in Japan. Several kinds of heat pumps and thermal energy storage are applied for heating, cooling and hot water supply. Cold energy is stored in ice storage tanks by a high efficient screw type chiller in the nighttime and discharged for cooling in the daytime. In winter, the GSHP generates hot water with lower output temperature around 35ºC mainly in the nighttime. The heat is stored in the concrete slab. In the summer season, the GSHP covers a part of the cooling load in the daytime. On the other hand, the GSHP is also used for preheating of hot water in the nighttime. The operation may be effective for recharge of ground temperature around the piles and lead to improve the COP during the cooling operation in the daytime. 1. INTRODUCTION Eight years have passed since millennium, there have been growing a sense of crisis about environmental issues, especially global warming all over the world. Reduction of CO2 emission has been recognized as the most important keyword in every field in Japan. In such environmental times, The Funabashi municipal rehabilitation hospital had started an operation in April, This hospital is introduced various energy-saving concepts about the heating and cooling system. So I assume this energy supply system for theme of this report. Generally hospital facilities need air conditioning for 24 hours and a lot of hot water for bathing of patients in the ward or washing works in the kitchen. Reduction of energy consumption for these heat demands is one of the most important issues in the design of hospitals. I adopted a main

2 design concept as reduction of CO2 emission when I designed, and I introduced the totally electrified heating and cooling system from the viewpoint of prevention of global warming. Because CO2 emission intensity at the time of electricity use is smaller than other energy use in the Kanto area (0.381kg-CO2/kwh,2004). And it is possible to contract with the electric power company that energy charge rate is discounted only using for heat storage in the nighttime. Therefore introduction of the totally electrified heating and cooling system contributes to not only a concept of reduction of CO2 emission but a purpose of reducing running cost. Several kinds of heat pumps and thermal energy storage system are installed in the energy supply system of this hospital. I will report mainly the contents of the above. 2. DESCRIPTION OF THE BUILDING This hospital is specialized in rehabilitation department to deal with physical impediment by cerebro-vascular diseases. In addition, this hospital provide intensive rehabilitation plans for patients from early period of onset, the hospital is trying to make patients come back to their original life early. This hospital was completed in December, 2007, and hospital was opened in April, Table 1 Overview of the building Item Contents Structure RC,S Number of floors 4 Total floor area 13,946.9 Building height GL+18m Number of beds 200 Photo 1 A photo of Funabashi hospital 3. DESCRIPTION OF THE HEAT SOURCE SYSTEM 3.1 The basic policy of the heat source system The operation time of air conditioning is clearly different by departments, because of the hospital characteristic. The heat source is needed for air conditioning and hot water supply respectively. I decided to adopt the totally electrified heating and cooling system, because I want to realize concepts that are consideration to environment, life cycle cost advantage system reliability

3 and safety. 3.2 The configuration of the primary equipment Main heating and cooling machine is a high efficient air cooled heat pump chiller (HHP) in this hospital. Exclusive cooling machine is a high efficient screw type chiller (SHP) that is storing cold energy in ice storage tanks (IHP). Exclusive heating machine is a high efficient air cooled heat pump chiller (EHP), exclusive heating machine for hot water supply is air cooled heat pump chiller (HWHP). Furthermore, Ground Source water cooled Heat Pump chiller GSHP or WHP is installed in this heat source system that is one of the main features for this heat source system. (Symbols in the parenthesis are used for the following pages.) 3.3 The operation concept of the heat source system The piping system for air conditioning is four-pipe system so that room temperature can be set freely. So fan coil units and air conditioning units in each room have two coils. I will note characteristic energy-saving concepts of this heat source system in a sentence of this next. Choice of the top runner model: It was a rule to adopt a kind of the high efficiency model, when we chose chillers for this heat source system. Aiming to the high efficient characteristic in partial load: HHP has the high COP in partial load, this characteristic contributes to improve performance of the whole heat source system. Improving the total COP of this system by choice of the most suitable temperature for heat source water: Hot water is heated in main hot water supply tanks after preheated in preheating tanks. HWHP heats preheated water up to 60, after makeup water from city water is heated to 38. Preheating is performed by WHP in summer nighttime, and by EHP in the other season and time. And this two stages hot water heating system contributes to reduce a initial cost in comparison with heating by only air source heat pumps for hot water supply. The effective choice of the electricity rate system: As a result of adjustment a part of heat source system operation to the discount terms of electricity rate, this operation contributes to reduce running cost of heating and cooling. Introduction of GSHP system: The detailed concept of this system is noted on the page of the next. I show specifications of the heat pumps in Table2, and a diagram of the heat source system in Figure1. Table 2 Heat pumps specification Main machine Number Specification Location High performance air cooled heat pump chiller (HHP High performance air cooled heat pump chiller (EHP (only for heating) High performance air cooled screw type heat pump chiller(shp) Ground Source water cooled Heat Pump chiller GSHP or WHP Air cooled heat pump chiller for hot water supply HWHP 11 Total cooling capacity 1,177kw Total heating capacity 1,298kw RF 3 Total heating capacity 354kw RF 1 1 Cooling capacity:490kw Max stored heat capacity 3,498kwh With three ice storage tanks Cooling capacity:50kw Heating capacity:62kw 3 Heating capacity:52kw RF Cooling unit: RF Chiller: Main machine room Ice storage tank: Outdoor machinery place Main machine room

4 HHP-1 (Air source HP) EHP-1 (Air source HP) EWHP-1 (Air source HP For Hot water supply) For hot water use places CT-1 Hot water storage tanks 5m 3 3 HEX-W1 Hot water preheating tanks 6m 3 2 THW-1 Water supply for hot water Hot water Supply/Return Chilled water Supply/Return PCD-1 PB-1 SHP-1 (Screw heat pump chiller) PH-2-1,2,3 M PC-2-1,2,3 M PC-1-IR1 PC-1-IR2 HEX-B1 Connected to the HEX-W1 Connected to the HEX-W1 HEX-B2 PB-2 ISU-1,2,3 (Ice storage tanks) WHP-1 (Ground source HP) PC-1-WHP PH-1-WHP Floor heating area Heat exchanger in PHC piles Figure 1 A diagram of the heat source system 3.4 The energy flow of the heat source system I show an assumed electricity input for the primary side of the heat source system, and show an assumed output heat from each heat source equipments, these data are shown in the energy flow (Figure2) for an annual integrated heat. The upper data of electric power supply in the figure2 means an amount of assumed electricity supply for HP in the daytime, the lower data means an amount of assumed electricity supply for HP in the nighttime.

5 Primary energy Electric Power supply Heat source system Heat supply Heat Utilization Using temperature Air source 1,604 2, HWHP EHP 236 (79) Hot water Preheating 60 (40) Electric power 742 HHP 1,585 Hot water (for AC) WHP SHP 13 (33) 739 (64) 590 Floor heating Chilled water Ground source (479) Ice storage -2 Units MWh [Annual total] Upper line Daytime supply (Bottom line) Nighttime supply Figure 2 Assumed energy flow of the heat source system 4. DESCRIPION OF THE GROUND SOURCE HEAT PUMP(GSHP) SYSTEM 4.1 The purpose of the introduction The GSHP system is provided in this heat source system. The GSHP system is more effective than air cooled Heat Pump system for operation in both of summer and winter. On the other hand, the characteristic that is effective for prevention of Heat Island Effect is an important concept of this system provision. And installation of heat exchanger which is made by polyethylene pipes in the PHC piles without digging extra holes is effective for an aspect of the initial cost reduction. 4.2 The outline of the GSHP system At first I note a component of the GSHP system. This system has two pairs of heat exchanger that is made of 20mm diameter high-density polyethylene U tube. 39 numbers of precast concrete piles (PHC piles) with 20m deep are used as ground heat exchanger. The GSHP equipment is installed in the main machine room. The water flow of heat source can be selected from the GSHP system to the central heat source system or to independent floor heating system. I show the operating mode of the GSHP system in summer and winter season in nighttime and daytime in figure 7 as a conception diagram. In winter season, the GSHP operate during the nighttime by cheaper electricity than daytime and supply 35 degrees hot water to the certain slab for floor heating and store the heat in the slab. If the temperature of the slab become less than 30, the GSHP supply hot water in daytime. The GSHP system can supply hot water to the floor heating pipes individually instead of the central system. Low temperature (about 35 ) of hot water can keep safe for prevent a moderatetemperature burn of the patient. And also the COP of the GSHP system can be improved by decreasing the temperature of hot water compare with 45 of central heat source system. In summer season, the chilled water from GSHP system is supplied to the central heat source system in daytime. At the same time, the GSHP system stores the heat under the ground and the

6 110.5m Figure 3 A range of the heat exchanger construction in PHC piles Photo 2 Double U tubes (heat exchanger) and PHC Figure 4 A conceptual diagram of the heat exchanger piles in PHC piles ground temperature become higher. The GSHP operate in nighttime by utilizing cheaper electricity and preheats makeup water for hot water supply. As a result, the GSHP pump up the heat from the ground, and the ground temperature is lower. Such kind of operating mode, the heat is transferred from the GSHP into the ground in daytime and this heat will be utilized to preheat the hot water in nighttime, is supposed to be a kind of Heat Storage System. And the heat is transferred from the ground into the GSHP in nighttime and this heat will be utilized to make chilled water in daytime, is supposed to be Cold Storage System. In other words, this is the plan to improve the COP of Heat Source System both the cooling and heating period by changing the mode between day and night. It is said that the heat storage characteristics of the ground make a negative effect for heat source system. But in this system, I paid attention to this characteristic and made a concept of improving performance.

7 Nighttime operating mode Concrete slab heat storage is using cheaper electricity at night Daytime operating mode Concrete slab emits a warm heat Winter season Summer season Night time operating mode Hot water preheating tank is heated, and soil is cooled at the same time, in the nighttime Daytime operating mode The WHP supplies chilled water, heats the soil at the same time in the daytime. Figure 5 A conceptual diagram of the GSHP system operating mode 4.3 Thermal response test When the main structure was constructed and the heat exchangers almost installed, we performed a thermal response test. The result of the test was fed back in numerical analysis of the GSHP system. 4.4 The estimate of the GSHP system COP in this operating mode We did numerical analysis about the GSHP system and predicted the COP of the system. We analyzed the numerical analysis with a design performance prediction tool. I show an operating condition on analyzing in the upper section and a result of analysis in the lower section in Table3. In the case 1, I set the analysis condition that the GSHP system supplies chilled water in summer season and supplies hot water in winter season. In the case 2, I set the analysis condition that the GSHP system supplies chilled water in daytime and preheats in nighttime in summer season, and supplies hot water in winter season. According to the result of analysis, the COP of the GSHP system could be expected to improve from 3.7 in the case 1 to 4.2 in the case 2 which was the condition of heat source system for this hospital. On the numerical analysis, a heat storage characteristic of the GSHP system contributed to improve COP. The system has been hoped that the data is measured at the time of the real using, is analyzed and is inspected.

8 Table 3 The estimate of the GSHP system COP in this operating modes Analysis condition Analysis result Notes Season Winter Daytime/ Nighttime Nighttime Daytime CASE1 Summer : For only cooling Intermediate season No operating Winter : Floor heating Floor heating for three hours Additional operating Floor heating for 15 minutes after 12 hours CASE2 Summer : Cooling and hot water preheating Intermediate season : No operating Winter : Floor heating Summe Nighttime No operating Hot water supply preheating r Daytime Cooling operating for 8 hours Cooling operating for 8 hours Season Object CASE1 CASE2 (Coefficient of performance) (Coefficient of performance) Winter Floor heating Cooling Summer Hot water supply preheating 4.5 COP (analysis result) is seasonal average. Conditions in the numerical analysis of hot water are preheated from 25 to 40, and quantity of water of 12m 3. Hot water supply temperature for floor heating is 35. Average initial soil temperature is Effective thermal conductivity of soil is 3.0w/m/K. 5. CONCLUSIONS (1) This paper introduced the construction example of totally electrical heating and cooling system that is combined with ice storage system. (2) Additionally this paper introduced the GSHP system used PHC piles as heat exchangers, reported the summary of the GSHP system and results of the simulation. So this paper showed that there is the possibility of improving the COP of GSHP system, if GSHP system is operated as short term heat storage mode. ACKNOWLEDGMENTS The authors would like to express appreciation to Funabashi city officials, hospital staff all member of the construction, Mr. Motohiro Okada who helped with translation, and Tokyo electric power company staff. NOMENCLATURES A: area [m 2 ], E: Electric power consumption of heat pump [W], G: Flow rate [m 3 /s], K: Overall heat transfer coefficient [W/m 2 /K], Q: Amount of heat extraction [W], r: radius [m], T: temperature [ ], t: Time [h], V: Volume [m 3 ], COP: Coefficient of performance of heat pump, [HHP]: High efficient air cooled heat pump chiller, [EHP]: High efficient air cooled heat pump chiller for exclusive heating machine, [SHP]: High efficient screw type chiller, [IHP]: Ice storage tanks, [GSHP]: Ground source heat pump chiller, [HWHP]:Air cooled heat pump chiller for hot water supply in the system Greek letters : Thermal conductivity [W/m/K], : Density [kg/m 3 ]