View from the rooftop

For a number of years now manufacturers have been predicting that air-conditioning in the UK’s domestic sector will grow massively. Their reasoning is simple. If, as is expected, our summers become hotter and longer, mechanical cooling will be the only way to stay comfortable, especially when it comes to getting a good night’s sleep.

It’s a scenario that is at odds with the government’s long-term plan to ensure that all new homes are carbon neutral in terms of the energy they use by 2016. So which is it to be?

Some outside the industry still argue against the use of air-conditioning. Yet in today’s commercial properties we simply cannot meet the demands of modern life and the requirements of legislation regarding fresh air and minimum and maximum indoor temperatures without some form of mechanical cooling and heating.

In commercial buildings we can insist that any equipment is the most energy efficient possible and that it is installed and maintained correctly, so that it provides the comfort levels needed while consuming the least amount of energy possible.

But there is simply no way that the government is going to achieve its targets for energy reduction if there is a significant growth in the use of air-conditioning within the nation’s 26 million homes.

The fact is that air-conditioning is not necessary in homes for the foreseeable future in the UK: there are other ways of reducing the internal temperatures of our homes. Mechanical ventilation with heat recovery, for example, has the ability to operate in bypass mode – in other words it pulls fresh, ambient air into the building while exhausting the stale internal air without recovering the heat. In the summer this can provide a degree of “free” cooling.

Without any form of cooling, computer modelling of a typical dwelling using CIBSE London weather data indicates that UK night-time bedroom temperatures will exceed 24ºC for up to 163 hours a year – approximately 20 days. If we model the same residential property, but include a heat recovery ventilation system, then the free cooling ability means that 24ºC will not be exceeded in any of the bedrooms between 10pm and 6am.

There is no way that the government is going to achieve its targets for energy reduction if there is a significant growth in the use of air-conditioning in the nation’s homes.

The benefit is that this type of ventilation system uses a fraction of the energy needed to run mechanical cooling and removes the problem of summer overheating. Mechanical cooling is therefore not necessary to maintain night-time comfort in the vast majority of our homes at the present time.

As we move towards 2016, building insulation and airtightness levels of new homes will increase further and this will have the beneficial effect of helping to reduce the energy needed for space heating by more than 50%. However, ventilating these houses will become more important. Using the same CIBSE weather data modelling, the forecast number of hours when a bedroom in one of these modern properties will exceed 24ºC during any night-time will rise to 690 without any active ventilation strategy. Assuming heat recovery ventilation is used and the free cooling mode activated, the number of night-time hours above 24ºC is again zero.

So is there a necessity for air-conditioning in the UK domestic market? I believe that while there is a momentum from certain quarters of the air-conditioning industry to develop a domestic market, this cannot be justified or sustained. Our modelling clearly demonstrates that the case for using heat recovery ventilation to supply mechanical cooling as required stacks up both technically and ethically.

There are two key questions surrounding this debate. Does the temperature increase attributable to global warming equate to an excuse for triggering a growth in domestic cooling; and will the UK government allow domestic cooling products to be sold in volume?

In answer to the first question, even with the projected increase in land temperatures, it will not be necessary to introduce air-conditioning into homes – unless they are properties located in “heat islands” such as large city centres, or properties that house people who are vulnerable during the heat of the day.

In terms of the government allowing the mass sale of cooling products for use in homes, it can only be a matter of time before government policymakers review all areas of power usage within domestic properties and introduce legislation through taxation and personal carbon allowances that will conclude the argument for itself.

There are problems with summer overheating but there are energy-efficient ways of solving these problems without resorting to a huge growth in air-conditioning within our homes.