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Benefits of warm air condensed

Most warm air heaters installed in the UK are non-condensing but this is set to change. Phil Brompton outlines the benefits that condensing units deliver
Condensing warm air space heaters currently account for a relatively small proportion of the warm air heaters installed in the UK. However, it is clear that legislation will make condensing technology mandatory within the next few years, delivered through future versions of the Building Regulations Part L2. At the moment, Part L2 requires a minimum nett efficiency of 91 per cent for these units, which can be met with non-condensing designs.

In fact, there is already pressure for the industry to go down this route. For instance, the criteria for including warm air space heaters on the Energy Technology List have changed recently. As a result, in order to qualify for Enhanced Capital Allowances, these units will need to operate in condensing mode with minimum full and part load efficiencies of 101 per cent (nett).

Timing is unclear

Currently, the timing of any move to mandatory condensing warm air space heaters is unclear but it is sensible to assume this will happen in the next two to three years and we are certainly gearing up for that.

In fact, as a company that manufactures both types, we don't have a particular axe to grind. However, I would suggest that a move to condensing for all warm air space heaters is something to be welcomed. For example, it has been estimated that around 18 per cent of the world's CO2 emissions arise from non-condensing boilers and heaters, so continuing with non-condensing units would certainly do the environment no favours.

And, of course, there are significant cost benefits for building operators, even when higher capital and installation costs are taken into account - as explained below.

Condensing warm air space heaters are not new to the market; they have been available for several years and thoroughly tried and tested in a range of applications. They can be operated on natural gas or liquefied propane gas (LPG) and are equipped with a secondary internal heat exchanger which extracts residual heat from the flue gases. This residual heat is transferred into the warm air stream for heating the space, thus increasing the unit's heat output without the use of additional fuel.

It is the secondary heat exchanger that accounts for the slightly higher cost of condensing units, compared to non-condensing.

Salvaging residual heat

Salvaging this residual heat, which would be wasted in a non-condensing unit, accounts for the increased efficiency of condensing units. It also reduces the temperature of the flue gases to below dew point, resulting in condensation - just as with the more familiar condensing boilers.

Consequently, provision needs to be made for safe disposal of the condensate via a drain point. Typical condensate production rates are 0.06 litres/kWh for natural gas and 0.03 litres/kWh for LPG.

In new installations a condensate removal system can be designed in from the start and will have a very small impact on installation costs. In a retrofit situation, where condensing heaters are replacing non-condensing units, provision of pipework to carry condensate away may be more complex and therefore cost a little more.

Nevertheless, as noted above, there are still cost benefits to installing condensing warm air space heaters that outweigh higher capital and installation costs to deliver a reasonably fast return on investment.

This can be illustrated by considering the running costs for a 140kW output gas-fired warm air space heater operating for 10 hours per day, 5.5 days per week during a typical heating season (prices based on commercial gas tariffs, August 2012), as shown in table 1.

As would be expected, the running costs of the condensing heater are less than those of the non-condensing versions. However, it is also important to take installation costs into account and these will vary considerably from one site to another.

For the purposes of this illustration, though, we can consider a modern well insulated building of, say, 2,500m2 floor area and a volume of 13,500m3 requiring the above 140kW heater. Typical end user customer installed prices would be as shown in table 2.

The cost difference of £1,400 could therefore potentially be recovered in less than two years when compared to a non-condensing heater with minimum efficiency levels.

Given that warm air space heaters should give at least a 10-year life - and many of ours have lasted much longer - the potential life cycle cost savings should be attractive to any building operator.

// The author is managing director of Powrmatic//
8 November 2012

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