Retrofit Home, Christchurch City
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House Details
- 130m2 floor area
- Built in 1940
- Single glazed, timber framed windows
- 200mm loft insulation
- 75% walls insulated
- No floor insulation
New Central Heating System
16kW air-to-water heat pump supplying hot water to radiators in each room.
11 DeLonghi PHD radiators, 1 towel rail; total 11kW at 55/45/20 (21kW at 75/65/20).
1 room thermostat in the lounge controlling the heat pump and thermostatic valves on each radiator.
The main living areas are heated to 21°C during occupied times with the bedrooms at 18°C and an overall night time temperature of 18°C. The system is controlled automatically to bring the house up to temperature before the occupants get out of bed.
Previous Heating
2x 6kW air-to-air heat pumps: 1 heating the kitchen dining area and 1 in the hallway providing some heat to the bathroom and 2 bedrooms, but virtually none to the lounge that was slightly offset from the hallway. 2 column heaters were also used when needed.
The lounge would be 10°C on a cold morning despite an air-to-air heat pump being less than 3m outside the lounge door which was offset from the direction the heat pump faced.
The lounge and bedrooms would be heated by column heaters in cold weather even when the heat pumps were running.
The 2 upstairs bedrooms were partially heated by heat from the kitchen/dining heat pump rising up the stairs.
Monitoring Results
| Month | Heat (kWh) | Power (kWh) | COP | Cost ($) @ 25c/kWh |
|---|---|---|---|---|
| Jul | 2242 | 794 | 2.82 | 199 |
| Aug | 2682 | 891 | 3.01 | 223 |
| Sep | 2070 | 669 | 3.09 | 167 |
| Oct | 741 | 224 | 3.31 | 56 |
| Total | 7735 | 2579 | 3.06 | Avg 161 |
228 kWh of heat was reabsorbed for defrosting over this period.
Overall COP = (7735 – 228*) / 2579 = 2.9 when defrost is taken into account.
Heating costs, assuming electricity at 25c/kWh.
Total electricity used by the house has gone up about 10% compared to 2013 when the house was last continuously occupied over the winter (The house had EQC repairs during the winter of 2014, and was unoccupied for 2 months).
However, not only was 2015 a cold winter but the whole house was warm in 2015 whereas before the central heating was installed, large parts of the house, in particular the lounge were never properly warm in winter.
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