Burning Issue: Single-room ventilation systems wasting resources

John Davison, managing director of Airtech Environmental Systems, cannot understand why single room heat recovery systems continue to be recommended as energy efficient products when the prevailing wind speed in the British Isles renders them totally ineffective
Burning Issue: Single-room ventilation systems wasting resources
WHILE government directives, regulations, initiatives and guidance direct manufacturers to comply with energy efficiency initiatives and encourage consumers to ensure they are as green as possible, millions of pounds continue to be wasted on ineffective ventilation systems.

It is probably true that the rise in the availability of energy-saving products has been matched only by the escalation of claims made about their performance. The problem is that all sorts of weird and wonderful methods are used to determine the energy performance and efficiency credentials of these products. Some of the data presented to highly reputable bodies, such as the Energy Saving Trust (EST), is misleading to say the least. Worse still, these figures have in some cases been accepted and used to form the basis of guidance to users.

One such example is single room heating recovery systems. Data supplied by some manufacturers to EST, upon which approvals are based, is technically flawed. Independent tests have proved these systems simply do not offer any benefits whatsoever in the UK climate. Used in social housing they will result in millions of pounds of taxpayers' money being wasted.

At the heart of the problem is the British weather. Most tests on the efficiency performance of ventilating equipment are carried out to 'free (still) air' with no wind resistance and yet figures available from the MET office show the average wind speed in the UK is about 5m/sec, enough to render single room HRV systems totally ineffective.

Independent tests, undertaken by BeataFlow, a leading British specialist ventilation/airflow research and development company, on a typical single room HRV unit of the type known to have been approved by EST, reveal that - even on boost - with an external wind speed of 5m/sec, no air whatsoever is extracted. In boost mode with an external wind speed of 7m/sec - a wind state which occurs frequently in the UK - the air flow through the unit is actually reversed and is blown back into the room unless it is (unrealistically) hermetically sealed. In trickle mode with an external wind velocity of 1m/sec - barely a breath of wind - almost no air is extracted: at wind speeds of no more than 3m/sec the air flow is again reversed and blown backwards.

Zero energy efficiency

Quite rightly EST bases its energy efficiency rationale on energy consumption and HRV units appear to perform well in this respect because energy calculations take into account claims that heat is recuperated and returned to the room. Total energy figures generally reflect the cost of running the unit less the value of the heat returned.

However, for this to be true air has to pass in both directions through a heat recovery unit, otherwise known as a heat exchanger, before any heat recovery can take place. The problem is that in typical British wind conditions no air is actually expelled through the heat exchanger because the average wind speed in the UK blows it back.

In reality, heat recovery during a 24-hour period could be negligible. Cold air would often be blown into the dwelling and this would be exacerbated by the air intake mechanism within the unit. Furthermore the HRV unit would be consuming electricity 24 hours a day.

With no extraction and no heat recovery it would be wise not to consider single room HRV systems either as energy efficient or to have any significant impact on reducing condensation.

Unfortunately the BRE (Building Research Establishment), the industry organisation charged with a responsibility for offering expert opinion, has advised EST in the Energy Efficiency Best Practice in Housing (EEBPH) scheme and documents under this banner continue to state that HRV systems should be installed. So it is no surprise that feedback from the market informs us that single room HRV systems continue to be perceived as energy efficient.

Yet the facts are unequivocal. Is not it time some of our so-called experts studied them so they can live up to their claim to offer impartial, authoritative information on energy efficiency techniques and technologies in housing?
1 March 2006


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