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Why should I choose to install a CO2 Heat Pump as my next Hot Water System?

This article covers 5 main reasons to invest in an energy efficient, CO2 heat pump water heater to replace an existing electric or gas storage hot water service.

1. It is the most energy efficient water heating technology, particularly in cooler climates

2. It is designed to work seamlessly with rooftop solar PV

3. It has the lowest operating cost ($0.36/day assuming 3kWh @ $0.12/kWh[1])

4. It is the quietest heat pump on the market

5. It employs an environmentally friendly, non-toxic, non-flammable, CO2 refrigerant


Heat pumps use less electricity than boosted solar hot water systems in cooler climates - chart by t2zero


1. Energy Efficiency In northern climates with year round solar availability, solar hot water systems are the natural choice for water heating. In cooler climates, they require supplementary boosting using gas (non-renewable) or (grid) electricity. The chart above compares the annual energy consumed by heat pump water heaters in Darwin, Perth, Sydney and Melbourne compared with the boosting energy required to supplement solar hot water systems in cooler months.

In Darwin, there is virtually no requirement for boosting – Solar is the best choice· In Perth, notwithstanding the need for boosting - Solar just pips heat pumps· In Sydney, the energy balance shifts in favour of heat pumps· In Melbourne (Victoria) the energy balance is strongly in favour of heat pumps

2. It is designed to work seamlessly with rooftop solar PV The Reclaim Energy CO2 heat pump water heater on average draws 1kW of power. As most modern rooftop solar PV installations have a peak capacity in excess of 3kW, they can easily meet 100% of the 3kWh/day (1kW for 3 hours) average energy required to run the heat pump. Running the heat pump during this time is an ideal way to self-consume excess solar PV generated electricity, effectively acting as a 3kWh thermal battery.

t2zero explains simply what a CO2 Heat Pump is and why it is the preferred heat pump for homes in the southern part of Australia.

3. It has the lowest operating cost The 3kWh/day required to run a Reclaim Energy CO2 heat pump water heater can be sourced entirely from rooftop solar PV, costing $0.36/day or $131/year on average to run. Electric storage systems employ a 3.6kW resistive element and take 3-4 hours to heat a tank of water using approximately 15kWh/day. Most electric storage water heaters run on a dedicated, controlled load circuit designed to take advantage of the cheapest electricity tariffs (off-peak). Assuming a tariff of $0.20/kWh (typical off-peak tariff) - $0.25/kWh (typical single-rate tariff), electric storage systems cost $3.00 - $3.75/day ($1,075 - $1,370/year) to run. The significant electric load required by electric storage systems (3.6kW) is generally well in excess of what a typical rooftop solar PV system can supply. A Reclaim Energy CO2 heat pump water heater can potentially save $940 - $1,240/year in energy costs compared with the cost of conventional electric storage water heaters under these assumptions.

4. It is the quietest heat pump on the market At 37dB at operating level, the REHP is truly whisper quiet. Heat pump systems employing refrigerants other than CO2 typically operate at much higher noise levels, an important consideration in higher density living environments, particularly when operating overnight.

5. It employs an environmentally friendly, non-toxic, non-flammable, CO2 refrigerant Heat pumps employ a variety of refrigerants. In 1988 the Montreal Protocol banned the use of Chloro-Fluoro-Carbons (CFCs) as refrigerants as they were discovered to be destroying the Earth's protective ozone layer. Today, commercial heat pump water heaters use Hydro-Fluoro-Carbons (HFCs) – typically R-134a[1] and R-410a[2]. While they have zero Ozone-Depleting-Potential (ODP), their Greenhouse Warming Potential (GWP) is >1,000x higher than CO2. Because of this, they will very likely face growing community pressure to be phased out. Other refrigerant options include Ammonia (R-717) and flammable Hydro-Carbons including Propane (R-290), Isobutane (R-600a) and Propylene (R-1280). CO2 (R-744) has been used as a refrigerant for commercial refrigeration applications for over 100 years. CO2 is non-toxic, non-flammable and environmentally benign. It was phased out in the middle of last century in favour of CFCs, however is very much back in vogue particularly for water heating applications. These factors coupled with superior performance in water heating applications have seen a resurgence in the use of CO2 as a refrigerant in heat pumps, particularly for water heating applications in cooler climates like Victoria. [1] The single-rate solar Feed-in-Tariff applying in Victoria from 1-Jul-2019

[2] Tetrafluoroethane – CH2FCF3

[3] Mixture of difluoroethane CH3CHF2 and pentafluoroethane C2HF5

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