Monthly Archives: November 2014


Heat without fire: heat pumps as a solution to carbon emissions

Heat pump

For today’s modern building design, heat pumps provide a competitive energy cost solution for space and water heating. While this is true for standard designs or retrofits with strong insulation specifications, the advantage in cost savings is even more distinct when heat pumps are integrated with the passive building concepts of air tightness and low-temperature heating design.

Where a design has a mechanical-ventilation heat recovery (MVHR) system, ASHPs may capture the extra heat energy in the building’s exhaust air for improved efficiency. This system is also likely to incorporate an auxiliary back-up from either an outside air or geothermal source (see Case Study A, below). Heat distribution networks may be a combination of air-air and air-water in ASHP installations.

Case Study A: certified passive house example

 Domestic heat-pump solution for detached 167m2, three-bedroom bungalow on exposed rural site, south-western Ireland. Passive timber frame construction; no stove; air-tight test: 0.56 N50

Passive House Space Heating Certificate 15kWh/m2 pa (10 W/m2) Space heating ambient temperature: 20°C constant year round. Constant DHW availability (52°C Top 180l DHW tank).

Heat-pump design: Integrated ASHP and MVHR unit. Space heating provided by air-air unit. Air to DHW unit with 180Ltr tank. 2kW geothermal auxiliary backup (winter-time operation) with integrated space heating through under-floor heating installed in bathroom and hall areas. Summer bypass valve for ventilation-only operation. 4.12m2 flat-plane solar thermal panels and 300l tank integrated with heat-pump system.

 Results for 2012: ASHP Air to Air COP: 3.4 and Air to Water COP 2.3

Annual Operation Periods:

Summer ventilation-only: 46%, Passive Recovery Unit: 54%, Compressor-on: 7.6%.

Energy consumption of ASHP, Ventilation fan and Solar circulation pump:

1200kWh/year or € 220.71 for constant DHW and 20°C space heat.

 Capital cost of heat-pump installation: €8,730 (+€2,760 on conventional oil-boiler installation)

Estimated payback at running cost difference (€1,100 per annum): 2.5 years.

John O’Sullivan, BEng Elec MA, currently works as a watch officer with the Irish Coastguard Service. He is also currently pursuing an MSc in Renewable Energy Technology Systems with Loughborough University through distance learning. O’Sullivan began his career as a merchant marine radio officer, mainly with the Dutch deep-sea merchant navy. He has overwintered on the British Scientific Base of Halley, Antarctica. In more recent years, O’Sullivan has worked as a project engineer in windfarm developments and has also worked as a consultant engineer in the area of ocean-energy development.