Heat Pumps

Now here’s a thing – you take a kW of energy (gas, heating oil or electricity) and normally you get a kW of “work” out of it – or in many cases much less than that due to various losses.

But – you stick a kW of power into a heat pump and something almost “magical” occurs – you can multiply the energy output by as much as 6 or even 7 times.  A Heat Pump uses high grade energy to extract low grade (or free) heat from a low temperature source (air, ground or water) and deliver it a a higher temperature into a treated space.

When used for comfort heating the operating principle is exactly the same as your domestic fridge – except in reverse – and most usefully the amount of energy output can be significantly greater than the energy input.  For those of you interested in technical details please feel free to email me or call for a chat. 

My interest in these systems arose because a nice Swedish chap called Hans Erikssen introduced me to a Heating Optimised Air to Air system that I have since specified and commissioned in many properties (village halls, church conversions, domestic and retail) here in Scotland with remarkable effect – both in terms of the ability to provide comfort heating and the savings achieved on energy bills – which is clearly something of a “win – win”.

Air To Air is simply the most thermally efficient use of a heat pump that I can think of – and in the case of the system developed by Hans – the system is heating optimised – which means it is not a glorified air conditioning unit – the functioning principle is shown below for ease of understanding – but bottom line these units are purpose designed to provide comfort heating and can handle everything the Scottish winter climate can throw at them.



In purely practical terms what you actually get hardware-wise is an indoor unit or units and an outdoor unit or units depending on the size of your space to be heated.  So for example, the Hay Memorial Hall in Cornhill which is roughly 20m x 10m x 6mH has two indoor and two outdoor units – here is a picture of each to give you an idea of the physical impact (which is small).

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And running costs?  Well here in Scotland which generally is a pretty cold and windy place to live these units will cost between £200 – £400 a year each to operate based on 24/7 running during the heating season – which again, based on rural Aberdeenshire (shivers!!!) is at least 36 weeks of the year.  Bottom line – these systems are not called Energysaver for nothing and if your property is suitable the savings to be accrued are substantial.  An air to air heat pump is not a cure-all but if it is suitable for your building then I will design a system for you, arrange for installation by experienced and competent fitters, organise the annual or 6-monthly filter cleaning if you can’t manage it yourself, and pop in every now and then to enjoy the warmth (scrounging a cup of coffee if you have a decent brew on the go).

Oh yeah – what do they cost?  Well the system shown above for the Hay Memorial Hall consisting of 2 indoor and 2 outdoor units, with an installed capacity of some 20kW came in at less than £7,000 fully installed and in terms of the heating oil savings paid for itself within 3 years.  Like I said – “win – win”. 

Air to Water (and indeed Ground to Water)

The HVAC industry is pretty unanimous that air to water heat pumps are the predominant heat pump product – certainly there are countless adverts making a whole host of claims in respect of performance and efficiency.  So it is only right that I cast my eye over these systems to give some ideas about what to look for and be aware of.  Ground to Water are less common and more expensive but many of the “issues” are common hence its inclusion here.

Operational issues with heat pumps which deliver energy to water are invariably caused by failings in the initial evaluation, or in the design itself, product specification, application and method of delivery of energy to the property, and finally in commissioning (which includes education of the end-user).  The same things happen in fossil fuel heating systems but many of the errors can be mitigated by the systems ability to deliver far higher temperatures than heat pumps – there is more margin for error if you like.  Heat pumps operate most effectively when delivering heated water at the lowest temperature possible which in turns means a higher COP (coefficient of performance).  So these are the “issues” to be taken into account.

  • Radiator sizing – low water temperature means over-sized radiators or special low water content / high thermal mass units – or underfloor heating;
  • Buffer vessels – very useful to prevent / reduce short cycling of the heat pump (compressors work best flat out for long periods);
  • Electric immersion heaters – many heat pump systems employ these to boost water temperatures – expensive and carbon intensive;
  • Specification – check the heat pump being offered works at the average winter ambient your property “enjoys”
  • Defrost mechanism – a heat pump takes energy from outside air but it can freeze – does it reverse cycle which is good or use an electric element or simply stop working?  Does your specifier / installer even know the answer?
  • Noise from the outdoor unit – should be 50dB or less to ensure no problems with neighbours;
  • Control – does the system operate under weather compensation for example for maximum efficiency;
  • System longevity, warranty etc.

Heat Pumps are worthy for consideration in many applications – however the phrase “buyer beware” has never been more appropriate – speak to an expert and not just an expert salesman.