Air Source Heatpump Case Study - Part 1

Heatpump testing, first 24 days

ZeroCarbonBritain's energy scenario, suggests a 50-60% reduction in building spaceHeating and hot water energy use through high performance building fabricand a 40% reduction in cooking, lighting and electrical appliances.

The average energy use per person in the UK as of 2012 was:

Space heating: 14.2 kWh/d/ppWater heating: 3.5 kWh/d/ppCooking: 0.6 kWh/d/ppLighting&Apps 3.3kWh/d/ppTransport: 17.4 kWh/d/pp

A 60% reduction in space heating and water heating 17.7 → 7.08 kWh/d/ppA further 3x reduction by using heatpump heating: 7.08 → 2.36 kWh/d/pp

A 40% reduction in cooking, lighting and appliances 3.9 → 2.34 kWh/d/pp

The total building electricity use therefore for the average person should be around:

4.7 kWh/d per person

(x2.34 = 11 kWh/d per household)

Heatpumps provide 65% of the heating demand in ZeroCarbonBritain multiplying the amount of energy for heating by ~3x from renewable energy.

MyHomeEnergyPlanner

Model suggests building fabric performance factor of 109W/K

Using SAP standard temperature of 21C + SAP heating profile Annual heating demand should be: 7318 kWhAt a COP of 3.0 the electric input should be 2439 kWh, or on average of 6.7 kWh/d.

This is almost 3x the ZeroCarbonBritain per person target for homes with heatpumps.

MyHomeEnergyPlanner: Retrofit

To achieve consistently warm temperatures and reach the target of 2.34 kWh/d per person for heating I would need to carry out a retrofit.

If I insulated the walls with 200mm of hemp lime, insulated the floor with 150mm of insulation, increased the loft insulation to 250mm and put in better doors I should be able to achieve:

61 W/KAnnual heating demand of: 3903 kWhAnnual heatpump electric input of 1301 kWh3.6 kWh/d per person.

I would need to superinsulate with 250mm of insulation on the walls to achieve a modelled electrical energy demand for the heatpump of 2.36 kWh/d per person.

Keen to try and achieve near this – long term project.

Was heating with direct electric heating.

Heatpump cost just over £3k

Retrofit cost ~ £15-20k?

Starting with a heatpump as its better than direct electric in the short term

From October 17th to November 10th: 24 days

Electric input: 88.9 kWhHeat output: 260 kWh

Average COP 2.92

Average daily electrical input: 3.7 kWh/d

October heating demand is close to annual averageIf I used on average 3.7 kWh/d over the year = 1.6x ZCB target... better than 3x!

Standby?

Standby energy consumption, power consumption less than 40W, 30W typical: 8.8 kWh

Average COP when heatpump is running: 260 / (88.9-8.8) = 3.25

Portion of standby may be direct heating, portion may be recovered when heatpump runs. Compressor is slightly heated.

Average indoor temperature of this period: 16.8C (but 18-20C when I need it)

Average outdoor temperature:11.1C

Modelled gains: 118WMeasured heat: 451W

Building heat loss factor:(451W+118W) / (16.8C+11.1C)= 100 W/K

Ideas for improving COP further:

Heatpump is one of the smallest heatpumps you can get its 5kW heat output but its still very much oversized for the room its currently heating and so its cycling a lot and running at its minimum speed.

John Cantor's has the same heatpump and its heating a larger house. It often reaches above 4 COP even in much colder temperatures. The house is much larger and there are many more radiators + underfloor

The intention is to run the heatpump though to the main house to replace the oil heating allowing it to run for longer without cycling and therefore hopefully a higher COP will be achieved.

Less cycling will also mean less time spent at standby reducing the lost energy there.

Do we need smaller heatpumps?Can the standby power be reduced?

Standby would add up to a lot of energy consumption in a low energy home if the heatpump is left plugged in as recommended for the summer season.

Average UK grid intensity last 4 days: 320gCO2/kWh

Heatpump CO2 intensity on last 4 days grid: 110gCO2/kwh at 2.9COP

Gas heating CO2 intensity:

216gCO2/kWh240gCO2/kWh after 90% efficient boiler.

CO2

SAP grid CO2 intensity 519gCO2/kWh

Heatpump CO2 intensity at 519gCO2/kWh and COP 2.9 = 178gCO2/kWh.