Selection of a Low cost heating system for a passive house.

There are a number of options to heat a home when energy efficiency is designed into the build from day one. This statement is particularly true when one aims for the passive house performance standard using the PHPP (passive house planning package) software. When we moved into the house one will see from a previous blog that we started out with two storage heaters to heat the house with off-peak electricity with a capital cost of €70 (One storage heater was free and the other we paid €70 ).

Times have changed and the next energy crisis came along in 2022. We now have switched to a 1.6 kw air to air heat pump . These units are cheaper to run and more efficient than other types of heat pumps or heating systems. The other reason a dedicated home heating single unit was selected was to simplify maintenance. The hot water system is independent of the house heating.

One benefit of using an air to air heat pump to heat the house was the realisation that in Ireland when one returns home after being exposed to a damp cold climate it was difficult to thaw out quickly when the whole house temperature was 20/21 degree Celsius when using the storage heaters. By careful placement of the heat pump one room in the house is now at a higher temperature. This almost equates to a fireplace being available to help drive out the dampness one absorbed. We also noticed the room is used more frequently.

The room we selected was the kitchen/dining room. I feel it is important to ensure that the warm air the unit is blowing out does not interfere with the area one uses near or under the unit. This particular unit has an upward air circulation option that can limit this but we still installed it in an area that is not a functional working or sitting area.

To select the correct size of a heating source one needs to review the passive house PHPP software for your home. In principle the passive house standard selects the coldest day of the year for this calculation. In Ireland the PHPP software uses local climate data installed in the software to calculate the heating required for the house. This equates to approximately 1kw of heat for every 100m2 of floor area. As our home is 200m2 we needed 2 kw output on the coldest day of the year (similar to the power a toaster or hair-dryer uses for the coldest day).

The Air to Air heat pump we used was the RAS-B13J3KVSG-E internal unit and the RAS-13J2AVSG-E1. These were one of the most efficient and economical units I could find. The price of the unit was around €600. Installation was another €1000 approximately. There are designer internal heat pumps options available from the same brand if one want to make the unit a design feature.

How the heat pump works -All heat pumps harness the natural heat energy present in the environment, air-to-air heat pumps can amplify the input power, resulting in a higher output. This is known as the Coefficient of Performance (COP), which measures the ratio of output power to input power. A higher COP indicates greater efficiency, and air-to-air heat pumps typically have a COP of 3-4, meaning they can produce 3-4 units of energy for every unit of electricity consumed. The air to air heat we installed has a SCOP of 6.3 and the designed heating load for the year is 752kw/h per annum. This approximately equates to €25 a month for a 7 month heating season @23 cents a kw/h. The letters SCOP is a seasonal calculation for the full heating season. In our unit the COP can produce 20 degrees inside if the temperature is 7 degrees outside.

There is also a function to cool the house with an air to air heat pump when global warming arrives in Ireland. Ireland missed the global warming cycle this year (2024) so we did not need to use this function.

Part 2 -Installation, performance and lessons learnt after 1 year of use…to be continued…