PowerPoint Presentation

Title: Heat Pump Water HeatersVikas Ashwani MarkandaAuckland University of Technology Presented by:

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Present Scenario

Major Hot water consuming sectors

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Average annual household energy consumption in New Zealand20 PJ of Energy

Substitute to conventional methods of water heatingMust be environment friendly and CO2 emissions must be minimum.Must demonstrate good energy saving potentials.Must be cost efficient.Technology capable of doing so is, Heat Pump Water Heating

What is a Heat Pump Water Heater ?Heat pump water heater is a device used to supply hot water for commercial and residential use.

Heat pumps use the same technology to heat water as is used to heat rooms. Heat pump systems use electrical energy to move' the heat - they don't actually make' heat. This makes heat pump systems much more efficient than traditional electric or gas water heaters.

Working principle of heat pump water heater

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Challenges in use of technologyIf refrigerants like hydrofluorocarbon (HFC), chlorofluorocarbon (CFC) and hydro chlorofluorocarbon (HCFC) are used they are harmful for the environment.When operated in cold regions ranging from 10 to 20 0C, the ratio of suction pressure (low pressure) of the compressor to the discharge pressure (high pressure) was large.It lowered water heating capacity and resulted in poor system coefficient of performance (COP).Solution employed:The compression stroke is divided into two stages.Refrigerant is injected at intermediate pressure.Thermal insulation of hot water tank is improved.High efficiency gas cooler is used.CO2 is used as natural refrigerant .

A favourable system with improved COP when serviced in extreme cold conditions.Advantages:Reduction in greenhouse gas emissions as no hydrofluorocarbon (HFC), chlorofluorocarbon (CFC) and hydro chlorofluorocarbon (HCFC) were used as refrigerant.CO2 has a low boiling point. Hence, the systems must be designed to sustain service pressures of 100 to 150 atmospheres, as refrigerant surpasses the critical point.Disadvantages:Knowledge gap/future prospects:Twostage compression with refrigerant injection can effectively overcome the problems of high discharge temperature, low heating capacity and COP of heat pump water heaters in extreme condition. However, it still has the problem such as big temperature difference between water and refrigerant in condenser. In order to reduce the temperature difference, enhance the efficiency and decrease the discharge temperature, further studies can be conducted.

Performance analysis using CO2 as refrigerant:Various parameters were studied:Rotational speed of compressor.Inlet water temperature at gas cooler.Inlet air temperature at evaporator.Water to refrigerant mass flow rate ratio.Observations:The mass flow rate of the working fluid increased on increasing the rotational speed of compressor from 380 to 680 rpm. This resulted in higher work of compression being done.The pressure of the working fluid increased upon increasing the inlet water temperature at the gas cooler; and resulted in higher work of compression.On increasing the inlet air temperature at the evaporator, the pressure of the evaporator also increased. Thus, resulting in higher COP.With increase in water to refrigerant mass flow rate ratio a decline in COP was observed.

Conclusion Drawn:For a system consisting 4 kW compressor, 6 kW evaporator and a 10 kW gas cooler, the mass flow rate ratio of water and CO2 must be between 1.2 and 2.2 for best results.Hot water temperature above 60 0C can be generated at ambient air temperatures ranging from 1525 0C.The COP of the system was found to be between 2.0 and 3.0.Advantages of this simulation report:It demonstrated, how altering various operational parameters of Heat pump water heaters affect its performance.The best working conditions could be determined to acquire optimum results from heat pumps and loss of energy can be kept to its minimum value.

Heatpipe enhanced solarassisted heat pump water heater (HPSAHP)HPSAHP is a heat pump with dual heat sources.It combines the performance of conventional heat pump and solar heat pipe collector. There are 3 modes of operation.When solar radiation is low, it operates in heatpump mode.When solar radiation is high, it operates in heatpipe mode and do not consume any electricity.The hybrid mode which includes the combined operation of heat pump mode and heat pipe mode.

Observations:Heatpipe mode is better suited when water temperature < 30 0C and heat input density > 400 W/m2.COP decreases when water temperature exceeds 30 0C. Hence, switching the system to heatpump mode of operation is advisable when the water temperature exceeds 30 0C.Advantages:COP of the hybridmode operation is 3.32, which is fairly high enough compared to 2.58 of heatpump mode of operation.An increase of 28.7% is observed in COP of hybrid mode as compared to the COP of heatpump mode.The hybrid system operates without consuming electricity when solar radiations are high. Thus, minimising conventional energy consumption cost.Disadvantages:It requires more space as compared to traditional HPWH because additional solar panel is added to the system.The system must be installed such that sunlight is incident on the solar heating system. It cannot be kept in a closed dark room where access to sunlight is negligible.Future prospects:Further improvement in modelling of system is possible making the system more compact and portable, such that freedom of operation and movement is possible as per the convenience of the user.

Vapour injection technique

Observations:The VI in high temperature cycle (HTC) and low temperature cycle (LTC) exhibited different effects on cycle characteristics of a cascade system.The VI in LTC increased the capacity of the system; on the other hand, the VI in HTC increased the COP of LTC by reducing the overlap temperature (OT).Advantages:Implementing VI technique increased the heating capacity of the system by 12% and cooling capacity by 6%.Implementing VI technique ensured system reliability and capacity improvement.Disadvantages:COP of the system decreased by 6.6% when injection ratio was 16.7%.No significant improvement in COP of the system was observed.Individual cycle performances of HTC and LTC were increased. But, the overall system performance did not indicate any significant improvement.

Knowledge gap/ future prospects:

Cascade cycle system are difficult to investigate because of their complexity. The number of variables in a cascade system are twice to that of single cycle, and their interrelations were vague. Because of this, irreversibility increases. This difficulty of work recommends that further studies on the cascade cycle as well as VI technique should be carried out to improve the performance and understanding of various heat pump systems.

Two stage heating novel heat pump water heater

Its a special twostage compressor consisting two cylinders, with an intermediate refrigerant to cool its motor.Two streams of refrigerant of unlike temperature are used to heat the water in condenser. This, minimises the temperature difference between the refrigerant and water enormously. Advantages:As compared to the traditional twostage compression system, the COP of the new cycle system was improved by 17.43% at ambient temperature of 00C, inlet water temperature of 50C and outlet water temperature of 65 0C.

With increase in relative liquid injection mass; the COP of both two cycle systems increased slowly, but discharge temperature of second stage (new cycle system) decreased faster as compared to that of traditional twostage compression system

System OptimizationThe system optimization of air source HPWH, which including calculations and testing was conducted.It began with absorption of air energy at the evaporator which was then pumped to the storage tank. The condensing heat of the refrigerant was released by the coil pipe to the water side. A rotary compressor was used to heat the water from initial temperature to the set temperature 55 0C.Observations:If refrigerant filling quantity is too much, it will descend the heating efficiency.If refrigerant is not enough, the suction and discharge pressure will be low; resultingin weak heat flow.If condenser coil pipe is short, compressor suction/discharge temperature will be higher than rated.If pipe is too long, some length will be unused.In high ambient temperature, a stubby capillary performed betterIn low ambient temperature, a slender capillary is better.

Advantages:The importance of refrigerant filling quantity and its effects on the COP of the system was demonstrated in this report.The importance of ideal length of the condenser coil pipe and its effects on HPWH system was revealed.Changing refrigerant filling quantity and other variables as per seasonal changes (i.e. variations in atmospheric conditions like temperature, pressure, etc.); improves the efficiency and performance of the HPWH.Knowledge gap/ future prospects:This report did not use any mathematical approach to derive above results. This methodology can be engaged with an additional mathematical approach to derive moreempirical and precise results

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