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Developing of heating and cooling local heat pump and method for design

Zohrab Melikyan

     

     National University of Architecture and Construction of Armenia, Armenia


    

ABSTRACT

     Contemporary buildings are large consumers of energy. About 70% of energy carriers are used for heating, cooling, ventilation, air conditioning and other purposes of buildings. As a result, environmental problems and global climate worsening factors arose. To fight the natural problems energy saving technologies, such as solar water heaters, different types of heat pumps and other kinds of renewable energy technologies found rather wide use. But, in spite of advantages the mentioned technologies are characterized by serious disadvantages. At present wide implementation have found closed and open loop geothermal heat pumps. Nevertheless, they have serious disadvantages that limit their use: first, they need underground heat exchangers in form of rather long pipelines laid in special trenches. This requires rather large free area around the buildings which creates problems especially in towns and cities. Second, the construction of heat pump systems is rather complicated and expensive. For overcoming mentioned disadvantages, increasing energy and cost effectiveness of geothermal heat pumps operating in heating and cooling systems of buildings in this article a new structure of local, cheap, energy efficient and sustainable geothermal heat pump is suggested and the method for its calculation and design is developed.


Keywords: local heat pump, Geothermal Water- Ice Storage Heat Pump, heating and cooling systems, heat potential, melting ice

1. Introduction

As low temperature heat source for a geothermal heat pump instead of the ground can be used appropriate quantity of water, stored in underground tank. The stored water should contain enough heat potential for covering the seasonal heating demand of a house. The ground plays a role of thermal insulation and at the same time of additional heat source. During heating season, the heat pump takes heat from the stored low temperature water and uses it for heating of the house. As a result, the water in the tank gradually is cooled and at the end of the heating season completely turns into ice. The stored ice serves as cooling resource for covering summer time cooling demand of the house. Therefore, in this regime, the heat pump does not operate and saves energy. The cooling of the house is fulfilled by the cold water of melted ice, collected in the tank during heating season. Therefore, in summertime the heat pump does not work and only cold water's circulation pump works and consumes energy. The developed system is investigated on the example of a family house, located in Yerevan, Armenia climatic zone, which is characterized   by wintertime -19 ̊C and summertime +35  ̊C design temperatures. That means that Armenia is one of most power-consuming areas, which needs in mentioned kind of heating - cooling energy saving systems.


2. Description of Structure and Work of Developed Water Ice Storage Local Heat Pump

Figure 1 represents the structure of developed water- ice storage geothermal local heat pump. It provides inside comfort conditions in both wintertime heating and summertime cooling regimes.

In wintertime heating regime water - ice storage local heat pump operates in the following manner: The compressor (1) of heat pump and underground water-ice storage tank (2) are located outside of the served house (3). On the rooftop of the house a flat plate solar water heater (4) is installed, which, in the beginning of heating season, serves for preliminary heating of tank water by solar energy. For reducing heating and cooling loads, the walls and roof of the house are well insulated and the windows are with double panes. The heating and cooling system of the house consists of fan-coils (5) mounted inside the house and connected to hot water supply (6) and return (7) stands of the heating system. The compressor (1) of heat pump compresses the refrigerant gas up to the required condensation pressure and heats it to a high temperature. The hot gas from compressor (1) is headed into condenser (8) where transfers condensation heat to the heating water, returned from fan-coils (5). In the condenser, the returned water is heated, and by circulation pump (9) and stand (6) is directed to the fan-coils.








































Figure 1.  Scheme of winter heating and summer cooling system of a house with developed local heat pump


Liquid refrigerant from condenser (8) passes through the expansion valve (10) of heat pump, where drops its pressure and temperature and by pipe (11) enters into the heat exchanger block (12), immersed into the water of underground tank (2). Actually, the heat exchanger block (12) plays the role of the evaporator of heat pump. In the evaporator (12) cooled liquid refrigerant absorbs heat from stored water. As a result, tank water gradually is cooled during whole the season and liquid refrigerant turns into gas and by ? knee tube (13) is exhausted again into the compressor (1). The knee tube provides vacuum, which causes pulsation and helps the mixture of lubricating oil and refrigerant to return from evaporator into compressor. The last technique helps when the compressor is located higher than the evaporator. The compressor (1) takes refrigerant's cold gas from the evaporator (12) and, after compression, pushes it again into the condenser (8). Here the heating water absorbs the condensation heat of the compressed hot refrigerant and is heated up to a temperature, required by the heating system of the house. In the evaporator, cooled liquid refrigerant absorbs heat from the stored water and turns it into gas, which finally is sucked into the compressor and the heat pump cycle replicates.


 3. Method for Calculation and Design of Geothermal Water- Ice Storage Heat Pump






where, Qhd.seas.-seasonal heating demand of optimally in­su­­lated building, kWh/seas.; Gw- quantity of water that should be stored into the tank before the heating sea­son starts, kg; cp.w= 4.18 kJ/(kgoC) specific heat of water; tw.1- stored water’s initial temperature at the beginning of heating season, oC; tw.2- stored water’s temperature at the end of heating season, oC; βice=334 kJ/kg-water ice fusion heat (Volkow, 2005).

The equation (1) allows finding the quantity of water Gw, kg, which should be stored into the tank to provide enough heat potential for covering seasonal heating de­mand Qhd.seas., kWh/seas. For this purpo­se, the equa­tion (1) is changed into the following formula:       

           





Actually, should be taken into account that the heat potential of stored water be enough for providing the complete evaporation of liquid refrigerant in the evaporator during whole the heating season. From this point of view it is becoming necessary to establish correlation between condensation and evaporation heats of the heat pump. To find the function of mentioned correlation, the following thermal balance of heat pump is analyzed:  


















Obtained formula (6) helps to determine the required quan­tity of low temperature heat source, for producing the needed quantity of the high tempe­rature heat source. In the considered system as high tempera­ture heat sour­ce is the seasonal heating demand of the building, which is generated by the condenser of heat pump. Seasonal heating demand Qhd.seas depends on si­zes of the hou­se construction characteristics and cli­ma­tic con­di­tions of the area. The house should have double paned windows and be optimally insulated with δins=0.19m thick insulation material. The value of seasonal heating de­mand is calculated on the example of a single-storey family house, located in climatic zone of Armenia, by using the method published in (Melikyan, Egnatosyan, 2015). The sizes of the house are: length lb=12m, width bb=12m and height hb=3.5m and outside design temperature is tout= -19oC. It is clear that seasonal quan­ti­ty of heat, produced in the condenser should be equal to the seaso­nal heating demand of the served buil­ding. Calculation shows that seasonal hea­ting demand of the house makes: Qcond..= Qhd.seas = 9450 kWh/seas.  

During heating season, the heat pump rejects heat from low tempe­rature water, stored in the underground tank and uses it for building’s heating purposes. As a result, the tank’s water gradually is cooled and at the end of heating sea­son comp­­letely turns into ice with tw2 = 5oC. Replacing in the formula (6) Qcond. by Qhd.seas will obtain the equa­tion for determining quan­­­­tity of water Gw , kg, to be stored in the under­ground tank:









where 1.07–coefficient indicates that the volume of ice in 7% is higher than volume of water; ρw = 1000 kg/m3 is the density of water.

Special research (Egnatosyan, 2009) shows that any kind of heat pump by its energy efficiency can compete with a hea­ting boiler with COP= 90%, if the heat pump’s COP is at least=3.0. As the suggested water-ice storage heat pump, makes a part of building’s heating system, it is becoming necessary to find the appropriate real value of heat transformation rate of the suggested heat pump in compliance with heating system’s tem­pe­ra­tures regime. For finding the real value of trans­formation rate the thermody­namic cycle of heat pump which operates with ecology friendly refrigerant “R-134a” in the range of condensation tcond = 65oC and evaporation tev. = 5oC­ temperatures were analyzed.

4. Determination of Transformation Real Coeffi­cient of the Water Ice Storage Geother­mal Heat Pump

For deter­mination of the real volume of the water - ice storage underground tank, in the formulas (7) and (8) the real transformation rate μ for con­si­de­red heat pump should be used. It can be found by the help of heat pump’s thermodynamic cycle, plotted on dia­gram (i – logP) of “R-134a”, (Wilson, Basu, 1988). The mentioned diagram is shown in Figure 2.



Figure 2. Thermodynamic cycle of investigated water-ice storage heat pump


line “4-1a” – Evaporation process of refrigerant in the evaporator of the heat pump, line “1a-1”- Superheating of gas refrigerant in intermediate heat exchanger, line “1-2b”- Adiabatic ideal process of gas compression in compressor, line “1-2”- Adiabatic real process of gas compression in compressor, line “2-2a”- Superheated gas cooling process in condenser of heat pump, line “2a-3a”- Gas condensation process in condenser of heat pump, line “3a-3”- Gas condensate sub cooling process in intermediate heat exchanger, line “3-4”- Gas condensate isenthalpic cooling in expansion valve.

i1a=394 kJ/kg; i1=403 kJ/kg, i2=467 kJ/kg, i2b=448 kJ/kg, i2a=428 kJ/kg, i3a=296 kJ/kg, i3=287 kJ/kg, l=64 kJ/kg, qc =171 kJ/kg


































5. Operation of the System in Summer Cooling Regime and Method for Calculation

It was stated above that in summer cooling season there is no need in operation of the heat pump, as cooling source is ready in form of the ice, collected on the surface of "heat exchanger - evaporator". In the beginning of summertime air conditioning season, because of heat gains from building's inside aria in form of water, warmed in fan-coils, the ice starts melting and the pump (9) supplies icy water to fan-coils of the house. Icy water with initial temperature tw.in = 0  ̊C, in fan-coils absorbs inside heat from the house and is heated up to a temperature tw.fin which is near to the inside temperature of building. This water completely returns into the tank and the temperature of the tank's water in the beginning of next heating season becomes about 25  ̊C. So, the developed system provides highly efficient wintertime heating and almost free cooling in summer time. That is to say the system operates by complete energy regeneration principal. Therefore, the energy wastes are negligible.


6. Yearly Energy Consumption by Water-Ice Storage Geothermal Heat Pump Heating-Cooling System

In winter heating period the consumers of electricity are the compressor of heat pump and water circulation pumps. In summer cooling period only water circulation pumps are in work and consume electricity. So, the energy total consumption during a year  NH-C.syst   makes the following sum:






where: NHP.wint – heat pump’s energy consumption in win­ter season, kWh; NHP.sum – supple­men­tal energy consumption by “air to air” type domestic heat pumps in summer season, kWh; - energy annual con­sump­tion by water cir­cu­lation pump, kWh.











As was mentioned above, the value of seasonal heating demand of considered building makes:

Qhd.seas. =   9450 kWh/seas., and real value of transformation rate of heat pump equals to . Therefore,  
















where: Vh.s.w – volume of the water, circulating by the “condenser -fan-coil” circuit of heating system during hea­ting season, m3/seas; - pressure, developed by water pump equal to hydraulic resistance of heating system’s pipelines, Pa.










































During summer season, for house’s cooling, the melted ice water with volume Vw.tank =46.3m3 and with initial temperature tin= 0oC, circulates through circuit “tank-fan-coil-tank”. In fan-coils, the cold water absorbs inside surplus heat in quantity of seasonal cooling demand Qc.d.seas of the house. As a result, the house is cooled up to summertime design comfort 25oC tem­pe­rature and water in fan-coils is warmed and returns from fan-coils into the tank to be used as low tempe­ra­ture heat source for heat pump in the next heating sea­son. In order to find the cor­rect value of water’s tem­­pe­ra­ture, returning from fan-coils and stored in the tank, the following equation is used:  







where: tw.fin and tw.in =0oC– final and initial temperatures of water in the tank during cooling season;

Qc.d.seas.­= 3490kWh/seas – seasonal cooling demand of considered example of house (Melikyan, Abd Elhaleem, 2010); Gw.tank= 46300kg – designed quantity of water, stored in the tank.

By given above data and equation (18) the following final temperature of water was found:






The calculation shows that the seasonal cooling de­mand of the house is enough to heat the cooling icy water in fan-coils from 0 oC up to 64.9oC. Actually, it is impossible, as the heating medium (inside air) temperature is only 25oC. Therefore, it is obvious that initial temperature of stored in the tank water at the beginning of next heating season is to be assumed equal to summertime inside comfort temperature of the house. For cooling purpose of the house, the pump takes whole 46.3 m3 icy water and pumps it from the tank to fan-coils of the house. To check the adequacy of the icy water cooling potential Qcool.pot to the seasonal cooling demand, the following equation is used:  






 It is clear that the cooling potential of the water is not enough for complete covering of the summer time cooling demand, which makes   Q c.d.=3490 kWh/seas. Therefore, available cooling capacity of tank water makes only 38.7% of seasonal cooling demand. The deficit of the cooling potential makes: ΔQcold =3490-1344 = 2146 kWh/seas.

The simplest and cheapest way to solve the problem of the deficit is the installation of two “air to air” split type domestic air conditioners with 1.1 kW electric power each (Carrier, 2016), and 2.2 kW of total cooling capacity. As these air conditioners perform during 919 hours of 1500 hours of the cooling season, consequently, their seasonal energy consumption makes 2.2 kWx919h = 2026 kWh/seas.

Thus, the total annual energy consumption by ice sto­ra­ge heat pump heating - cooling system of the building makes:





The yearly consumption of energy, referred to 1 m3 of the house makes 11. 15 kWh/(m3 year). Such a low specific consumption of energy proves the high energy efficiency of developed technology.


7. Conclusions

The suggested Water-ice storage geothermal heat pump heating and cooling system of houses can find wide application because of its rather simple structure and high energy efficiency. The proposed method for calculation and design can be accepted by designing enterprises to implement into practice designing of simple and cheap local heat pump structures to achieve advanced technological solutions in the field of round year heating and cooling of buildings. Actually the new system is a diversity of local type of geothermal heat pump heating and cooling system.  

The water storage tank does not need thermal insulation, as it is located in the ground, which plays the roles of both insulation and partial heat source. The 5575 kWh annual consumption of electricity for both heating and cooling of the house with 500 m3 of volume, that is to say 11.15 kWh/ (m3 year) indicates the high energy efficiency of suggested system. As the system round year operates by energy regeneration principal, the energy wastes are negligible. As a result, the system provides highly efficient wintertime heating and inexpensive cooling in summer period.

Compared with open and closed loop heat pumps the developed local heat pump does not cause environ-mental damages e.g., erosion, sedimentation, toxic antifreeze solutions, etc. The proposed method and formulas for determination of correlation between high and low potential heat sources is helpful for heat pump designers. In case of experimental verification and confirmation of anticipated results the suggested system probably will squeeze out the application of contemporary well known open and closed loops geothermal heat pumps. The bigger the served building and the colder and longer the heating season, the larger the water storage tank. Analysis show that in most cases, the volume of the tank makes about 9.5 to 15% of the served buildings and does not occupy free areas of yards of buildings.     


REFERENCES

Air Properties-Temperature, density, specific heat, thermal conductivity, expansion coefficient, kinematic viscosity and Prandtl's number. http://www.engineeringtoolbox.com/air-properties-d_156.html [accessed on: 20.07.2016]

Catalog, 2016. Domestic air conditioners, Carrier, 55, www.carrier-aircon.ru [accessed on: 15.05.2016].

Egnatosyan, S.M., 2009. Hybrid System for Heating and Cooling of Houses with "Air to Air" Heat Pump and Heating Boiler. The 4th International Renewable and Clean Energy Conference Yerevan, 41.

Kopko, V.M., 2014. Heat supply and ventilation. 2nd edition, Publishing house "ACB", Moscow, 336p, ISBN 978-5-93096-890-6.

Marriott, M.J., Featherstone, R.E., Nalluri, C., 2009. Civil Engineering Hydraulics. 5th Edition, University of East London, J, Wiley & Sons, 424p. ISBN-10: 1405161957, ISBN-13: 978-1405161954.

Melikyan, Z.A., Egnatosyan, S.M., 2015. Residential Buildings: Heating Loads. Encyclopedia of Energy Engi-neering and Technology, Second Edition. Taylor and Francis: New York, 1629-1636. Published online: 17 Jun. DOI: 10.1081/E-EEE2-120051988.

Melikyan, Z.A., 2012. Heating-Cooling of Buildings. Efficiency of Conventional and Renewable Technologies LAP Lambert Academic Publishing, Germany, 344 pages ISBN-978-3-8443-1939-2.

Melikyan, Z.A., Ali Abd Elhaleem A.F., 2010. Assessment of a modi?ed method for determining the cooling load of residential buildings. International Journal Elsevier V.35, England, 4726-4730.

Volkow, A.I., Jarskij, A.M., 2005. Chemical Large Guide. Publishing house "Soviet school", Moscow, 608.

Wilson, D. P., Basu, R. S., 1988. "R134a".  ASHRAE Transactions. Vol. 94 part 2. CoolPack- software collection of simulation models for refrigeration systems, developed by the Department of Mechanical Engineering (MEK), Section of Energy Engineering (ET) at the Technical University of Denmark (DTU).


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Journal of Buildings and Sustainability - 2016 - Volume 1, Issue 1