A lot of hot air?


More concerning — and the article was headed “working with nature” — was that among a number of highlighted features were “the installation of five heat pumps in . . . the bedrooms, lounge and kitchen”.
I sometimes wonder how we have reached the point where so-called heat pumps are seen as a positive, even environmentally-friendly feature.
For many years I arranged the installation of what were described as split-system or reverse cycle (heat in winter and coolness in summer) air conditioning units into leased commercial buildings.

This was an economic way of providing acceptable working conditions in offices throughout the 80s and 90s where a central ducted system was inappropriate for short-term leased space.
I have no doubt that the modern split system unit, now always promoted as a “heat pump”, is more efficient than those I installed by the hundreds during previous decades. However, I’m not convinced that they can be called environmentally friendly when used as a residential heating/cooling system. I’m not even sure they can be called a heat pump.

For a start, the whole idea of air conditioning a home in New Zealand’s mostly mild climate knocks it out of the park before you even consider its efficiency. 
Simple fact: If you have it you will use it. If you install air conditioning you will use it and soon find that you cannot accept even the slightest discomfort during winter or summer. You become accepting of a standard, even temperature of 20°C of artificially filtered, dehumidified air, and soon nothing else will do. Brisbane yes. The North Island of New Zealand? Hardly ever.

I accept that for some people air conditioning helps compensate for a badly insulated home, reduces condensation if the house is poorly ventilated and reduces allergic reactions from pollens. But environmentally friendly? Not even close.
And are those glossy wall-mounted air conditioning units, touted on television by a range of past and present sports stars, really heat pumps? If you can call a compressor a pump and you can describe an air-sourced condensing unit in that way then maybe you can — just.

Air-sourced heat pumps are relatively easy (and inexpensive) to install and are, therefore, the most widely used type of heat pump.
However, they suffer limitations due to their use of the outside air as a heat source or sink, plus varying efficiency under different and changing weather conditions. Sounds like most of New Zealand doesn’t it?

Arguably the weakest part of the equation is that the typical residential heat pump installation does not, on its own, provide a source of fresh air — and certainly not filtered fresh air.
Being, by its very nature, a non-ducted, recirculating system, it requires the home owner to open windows and doors if they don’t want to simply recirculate the same stale air over and over again.

This rather reduces the reason for having air conditioning in the first place, and certainly reduces the efficiency of the installation.
Another concern with residential air conditioning systems is the potential for home owners to overlook the need to maintain both the air handler and the condensing unit on a regular basis.
If filters are not regularly cleaned and replaced, and pumps and heating elements not serviced, the efficiency drops alarmingly.

The rather negative results of a recent BRANZ survey on general home maintenance does not help instil confidence in our ability to wash down walls regularly, let alone manage a maintenance regime for something that, on the surface, at least trundles along happily for years.
As I walk around my inner-city Auckland suburb, I see a growing number of condensing units sitting outside 19th Century cottages and villas.

The statistics show that we are not that good at insulating our older homes, even with the quite generous government subsidy available. Again, the efficiency of an air conditioning system is significantly compromised if the space it serves lacks insulation.

Nevertheless, I understand the attraction of being able to switch on a heat pump and instantly bask in warm, dry air in winter and cool air in summer. Just don’t try to convince me it’s helping the environment.

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