So How the Hell Does a Heat Pump Work?

It’s a complicated process!  A miracle of science!!  And of course you’ll need to know all about the laws of thermodynamics to really understand it…

…but here’s how a heat pump works, in a nut shell.

Layout for a ground source heat pump - tapping into the sun's heat stored in the soil.

It's starting to get colder out there, so we’re starting to flick the heat on indoors.  We’re currently working on a some new-build houses in Dublin and Meath and are assessing options for heating and the efficiency of these systems through the use of renewables.  Often when we talk to people about how heat pumps can keep your home warm in winter, they get a look of bewilderment on their faces and ask how can that be possible.

People don't usually tell us that they're confused about how a fridge or air conditioner works, even though it's the same exact process - moving heat from a cooler area to a warmer area.

Heat pumps transfer heat by circulating a refrigerant through a cycle of evaporation and condensation.   The refrigerant is the medium that transfers the heat.  A compressor pumps the refrigerant between two heat exchanger coils. In the first coil, the refrigerant is evaporated at low pressure and absorbs heat from its surroundings (outside). The refrigerant is then compressed as it passes to the other coil, where it condenses at high pressure. It then releases the heat it absorbed earlier in the cycle - usually into the water of your heating system.

But this is Ireland.  It’s winter.  How on earth does it get heat from the outside air?

As the ground and air outside always contain some heat, a heat pump can supply heat to a house even on cold winter days. In fact, air at –18°C contains about 85 percent of the heat it contained at 21°C.

Heat flows whenever you have a temperature differential.  Maybe it’s that we have blinkers here due to our experience with cold outdoor temperatures. When we go outside in winter, our bodies will have a much higher temperature, being at about 37°C, and we then experience cooling. We’re always cooled off by cold outdoor air, so it is hard to imagine that that same air could ever heat anything else up.

The basic physics here is that heat will flow from something warmer to something cooler.  The answer is that, through the physics of the refrigeration cycle, as long as you can lower the temperature of the outdoor air, you can extract useful heat.

The vapour compression cycle

A heat pump exploits the fact that a fluid’s boiling point is affected by pressure. Lowering the pressure lowers the temperature at which the fluid evaporates, changing from liquid to gas: raising the pressure raises the temperature at which it condenses, changing from gas to liquid.

1. Refrigerant in the evaporator is colder than the heat source. This causes the heat to move from the heat source to the refrigerant as it evaporates.
2. This vapour moves to the compressor where its temperature and pressure are increased.
3. The hot vapour now enters the condenser where it rejects heat as it condenses.

The refrigerant then moves to the expansion valve; drops in temperature and pressure; then returns to the evaporator.

The basics of the Vapour Compression Cycle.

Ground source heat pumps

Use a 'closed loop' system of water/anti-freeze to collect the soil heat. Air/water heat pumps collect heat from the outside air. Generally, air temperatures are moderate in Ireland but due to natural frosting of the air heat exchanger during heat collection, it is necessary that these pumps use a small amount of energy to defrost. This leads to a marginal decrease in performance which is offset by a low installation cost.

The initial capital costs of installing a geothermal heat pump system is usually higher than other conventional central heating systems. A large proportion of the outlay will be for the purchase and installation of the ground collector. The system is among the most energy efficient and cost effective heating and cooling systems available.

Typically, 3-4 units of heat are generated for every unit of electricity used by the heat pump to deliver it, and the payback is typically about 8-10 years. The life expectancy of the system is around 20 years. Once installed a heat pump requires very little maintenance and anyone installing a heat pump should speak with their installer regarding a maintenance agreement. Heat pumps operate optimally when a system design approach is taken. It is important that the heat collector and heat distribution systems are correctly sized/installed.  (Refer to top image).

Air to water heat pumps

The evaporator collects heat from the outside air, which is then drawn into the unit by the fan through the evaporator fins and expelled through the front grille. The evaporator has liquid refrigerant passing through it, which is at a considerably lower temperature than the outside air, therefore the air gives up its heat to the refrigerant, which then vaporises.

This preheated vapour now travels to the compressor where it is compressed and upgraded to a much higher temperature.  Cooler water and the now cooler refrigerant returns to its former liquid state but still under high pressure from the compressor.

This high pressure is then released by passing the liquid through the expansion device and from there it returns to the evaporator and the cycle starts again.

Compared with central Europe (where air source heat pumps are already very popular), Ireland has a relatively moderate winter climate. With average winter temperatures of around 5°C, seasonal Co-efficient of performance ( or Efficiency) comparable with ground source (or Geothermal) heat pumps are achievable, without the additional cost of expensive ground loop systems having to be installed in the garden.

What Hofler Architects can do…

We regularly specify heat pumps and other renewable systems for the new-build and domestic extension projects we undertake.  Early in the design stage of a project we are considering which type of renewable technology will work best with the particular needs, the budget and the short and long-term costs.  We will carry out a number of BER studies - (Building Energy Rating) to look at all combinations of systems to determine which solution works best for you.

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Read an eloquent client testimonial here and what the Irish Times have said about some of our sustainable domestic renovation and extension work here.  

If you are planning to extend, renovate or build a new dwelling - Talk to us about your project.  You can contact us at any time here.

Return to our homepage or view our blog articles index page.

SP ACIOUSArchitects, Dun Laoghaire, Co. Dublin. 01-5585205

Tel: 01-2809322

NZEB - Nearly Zero Energy Buildings in Ireland

Today we've been at the nZEB-15 National Retrofit Conference at Dublin Institute of Technology listening to the latest research, developments and education in this energy retrofit technology for Irish buildings.

Introduction video - Near Zero Energy Buildings

Some Information on Nearly Zero Energy Buildings standards in Ireland:

From January, 1st 2019 every new public building will have to be designed to nearly zero energy building standards. Also, all other new buildings will have to comply with the new nearly zero energy buildings standards from January, 1st 2021. This arises from the Recast European Performance of Buildings Directive 2010/30/EU.

For a typical dwelling this will equate to 45 kWh/m2/annum and an Energy Performance Coefficient (EPC) and Carbon Performance Coefficient (CPC) of 0.302 and 0.305 in accordance with the common general framework set out in Annex I of Directive 2010/31/EU on the energy performance of buildings (Recast). This takes account of the energy load for space heating, water heating, fixed lighting and ventilation. A very significant proportion of which will be covered from renewable energy sources produced on-site or nearby. (Ref: Towards Nearly Zero Energy Buildings in Ireland – Planning for 2020 and beyond. 

 The proposed improvement from current building  standards  to  an intermediate and final NZEB target for buildings other than dwellings are:

Targets will be further refined when developing new the technical performance standard TGD L – Buildings other than Dwellings. (Source: Towards NZEB in Ireland- Planning for 2020 and beyond)

Energy Performance of Buildings Directive (EPBD)

The EU Energy Performance of Buildings Directive (EPBD - 2002/91/EC) is the main European legislative instrument for improving the energy efficiency of Europe's building stock. Under the Directive, the following obligations were introduced in all Member States:

• A methodology to calculate and rate the integrated energy performance of buildings
• A system of energy certification for new and existing buildings, with display requirements for public buildings
• Regular inspections of heating and air-conditioning systems
• Minimum energy performance standards for new buildings and for existing buildings that undergo major renovation with a useful floor area over 1000m2

The EU Energy Performance of Buildings Directive (EPBD) was transposed into Irish Law from 2006 onwards.

From 2013, the EPBD was superseded by the Recast EPBD and S.I. No 666 of 2006 was superseded by S.I. 243 of 2012.  See more at: http://www.seai.ie/Your_Building/EPBD

Changes in the Building Regulations in Ireland

Building Regulations were first introduced in Ireland in 1976 in Draft form and revised draft Regulations were introduced in 1981. The Building Regulations were formally revised in 1991, 1997, 2002, 2005, 2008 and 2011.

There have been significant step changes in the Irish Building Regulations since 2005. Technical Guidance Document Part L (TGD L), of the 2008 Regulations required a 40% reduction in primary energy use compared to a reference dwelling specified in the TGD Part L 2005 Regulations. TGD L of the 2011 Regulations require a 60% reduction in the primary energy us. The gradual improvements leading to NZEB standards for dwellings are summarised in the table below. 

*These energy values are for a typical two storey semi-detached house.

Information from NZEB Open Doors Ireland.

Ireland's Largest Strawbale Building!

The Lime House guesthouse featured on RTE Nationwide.

Ireland's largest strawbale building designed by Paul Mulhern of SPACIOUS Architects is nearing completion at the Rock Farm, Slane Castle, Co. Meath.  The project was featured on tonight's Nationwide program on RTE (12 mins in). Finishing touches are being put to the eco guesthouse in preparation for the weekend's concert.  The program is available to view on RTE's Player for the next 20 days.

Rock Farm site plan at Slane showing all six straw bale buildings.

The Lime House is the Rock Farm Slane’s 2-storey, 6 bedroom eco guesthouse, which has been built out of straw bales and clay plaster with lime on the outside to provide healthy, environmentally-sound eco-tourism accommodation in the Boyne Valley. This guesthouse has been designed to the highest environmental construction standards, and in sympathy with the woodland, organic farmland and architecturally-protected parkland of Slane Castle just over the river from the development.  The Lime House is named after the adjacent stone ruins of a lime kiln which now forms a centre-piece of the new courtyard space to the front.

The Lime House and five other straw bale buildings including a rental cottage, worker's cottage, farm office and a family house for the owners were all designed by architect, Paul Mulhern.  The guesthouse, farm office and yurt camping are all now complete.

The rear of the Lime House, facing the farm.

Elevation drawing.

Side Elevation.

Perspective drawing of the Lime Home.

Strawbale, lime plaster, recycled timber materials.

• The Rock Farm, Eco tourism farm, Slane.
• Straw bale building.
• SPACIOUS Architects.  01-5585205

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[Designed while Paul was a partner in his previous practice].

Passive House Principles Simply Explained:

With Dun Laoghaire Rathdown and Dublin City Councils set to make Passive House standards mandatory for new buildings in their forthcoming Development Plans - 

“The time has come in Ireland for passive house standards to move from the margins to the mainstream, for building policy and its energy efficiency to become more active by becoming more passive... " - Pat Cox

Passive House or "Passivhaus" buildings provide a high level of occupant comfort while using very little energy for heating and cooling. They are built with meticulous attention to detail and rigorous design and construction according to principles developed by the Passivhaus Institute in Germany, and can be certified through an exacting quality assurance process.

The new-build Passivhaus Standard requires:

• a maximum space heating and cooling demand of less than 15 kWh/m2.year or a maximum heating and cooling load of 10W/m2
• a maximum total primary energy demand of 120 kWh/m2/year
• an air change rate of no more than 0.6 air changes per hour @ 50 Pa

The Passivhaus refurbishment standard, EnerPHit, requires:

• a maximum space heating and cooling demand of less than 25 kWh/m2.year or a maximum heating and cooling load of 10W/m2
• a maximum total primary energy demand of 120 kWh/m2/year + heat load factor
• an air change rate of no more than 1.0 air changes per hour @ 50 Pa

To achieve the Passivhaus Standard in the Ireland typically involves:

• very high levels of insulation
• extremely high performance windows with insulated frames
• airtight building fabric
• ‘thermal bridge free’ construction
• a mechanical ventilation system with highly efficient heat recovery

Just bear in mind though:

"It is far more difficult to be simple than to be complicated; far more difficult to sacrifice skill and easy execution in the proper place, than to expand both indiscriminately".  John Ruskin.

Passive House Ireland - Facebook

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