Partners in energy efficiency

Published:  04 August, 2010

underfloor heating, UHMA
The benefits of the scrapping of the Low Carbon Buildings Programme — Chris Ingram.

Chris Ingram hopes there are signs of new thinking in the new Government’s approach to carbon reduction as it comes into office vowing to make cuts in public expenditure.

While, as I write, the mighty axe itself has yet to fall, one or two practice swings have already made a start on clearing the deadwood.

Among the very first to fall was the Low Carbon Buildings Programme, which since 2006 has provided about 20 000 grants for the capital and installation costs of micro-generation equipment.

Although the size of the cut — just £3 million, which is pretty much loose change for a Government department — gives me a very cold feeling about what is to come, I cannot join in the howls of protest that have greeted the announcement.

Indeed this cut may be the first dull glint of a silver lining. I take it as a gleam of hope that the coalition will take new attitude to energy saving, one that realises the importance of integrating technologies. I hope so, because unless we realise that only integrated systems can cut carbon emissions, we will continue to waste money and energy.

For reasons known only to itself, the last Government chose to ignore the fact that heat pumps and condensing boilers only work at maximum efficiency with low-temperature emitters.

Condensing boilers depend on low return-water temperatures (55°C or lower) to remain in condensing mode for maximum efficiency. Traditional high-temperature radiator systems with typical 80°C flow and 70°C return struggle to meet these conditions. In a concrete floor construction an underfloor heating system requires a flow temperature of around 40°C, making it a perfect companion for the condensing boiler.

Heat pumps also require low return temperatures for maximum COP.

Pretty much all the energy initiatives from the Labour administration, including the LCBP, focused on the heat source and not the heat emitter. To achieve real energy efficiency, both have to be integrated into a low-temperature system — such as underfloor heating.

All the incentive schemes and endless talk of more efficient boilers and renewables such as heat pumps will never make Britain a greener place in which to live unless they are combined with a reliable, low-temperature emitter. Without that, all those hi-tech heat sources will give is a lo-tech performance.

As result the UK has tens of thousands of condensing boilers that hardly ever condense and thousands of inefficient heat pumps.

Warm-water underfloor heating can boost efficiency of boiler-based systems by 20% and can be even more effective when used with heat pumps. Such savings simply cannot be achieved with high-temperature radiators.

Underfloor heating provides these savings for a variety of reasons. First and most fundamental is that a much high proportion of the heat emitted by UFH is radiant, rather than convected, as with the ill-named radiator. The nature of radiant heat means that the same level of comfort can be achieved at a lower air-temperature, so thermostats are typically set one or two degrees lower — reducing energy consumption.

The room requires less heat for the same comfort level, and demand on the heat source is lower.

underfloor heating, UHMA
The low flow temperatures that are characteristic of underfloor heating enable condensing boilers and heat pumps to operate at maximum efficiency. (Photo: Timoleon)

The other critical factor is the flow temperature of the water in the heating system. Underfloor heating can be designed to work with water temperatures as low as 30°C, although 35 to 40°C would be more typical with floor coverings such as wood and carpets.

Radiators, on the other hand, typically require 45°C plus for what are euphemistically called ‘low-temperature’ radiators and in excess of 65°C for ‘standard’ radiators. Renewable heat sources such as heat pumps can provide ‘radiator levels’ of hot water, but their efficiency is significantly compromised (note my italics again).

To illustrate this point, a heat pump providing 35°C water could have a COP of 4, but an increase in water flow temperature to 45°C reduces the COP to just 2.5).

The only alternative is to fit oversized or ‘low-temperature radiators’. Typically these need to be twice the size of a normal radiator and require a flow temperature of at least 45°C, often in excess of 50°C, with a corresponding significant reduction in the energy efficiency of the whole heating system.

No matter what the heat source, UFH is more efficient

UHMA anticipates that the warm-water underfloor heating market may actually benefit from the closure of LCBP, believing that like other energy saving legislation it was fundamentally flawed.

LCBP put the sole emphasis for efficiency on the generation of heat, completely ignoring the vital roles of controls and the heat emitter.

 

If the coalition Government wants to make real progress towards the carbon-reduction targets it must promote a whole-system approach to the way we heat our buildings, rather than investing huge sums of money in just one part of the system.

Chris Ingram is chairman of UHMA, the trade association for surface heating and cooling.

 

 



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