Looking for energy savings can get you into hot water

Published:  12 August, 2008

A ground-source heat-pump system at Mitsubishi Electric’s headquarters at Hatfield is linked to closed-loop coils laid in trenches to extract energy from the ground and help the system perform over 300% more efficiently than a traditional chiller/boiler combination.

While you cannot avoid using energy in the built environment, it is perfectly possible to take control of those energy costs — and benefit the environment into the bargain. Philip Ord looks at the potential of heat-pump VRF systems — and explains the significance of the headline.

There are few who now argue against climate change as an accepted reality but regardless of whether you do subscribe to the ‘green’ debate or not, the rising costs of fuel offers the potential of tremendous financial benefits for businesses that examine their building’s energy use and find ways to cut consumption.

As part of our Green Gateway Initiative, we advocate a general look at where your building consumes energy and an audit to find ways to reduce consumption. This need not be an expensive exercise, as simple things such as better or more regular maintenance for plant can make a real difference.

However, there is one area where dramatic differences can be made — and that is in the provision of heating and hot water to commercial buildings.

Whilst we may all be thinking of keeping cool at this time of year (we live in hope of a proper summer), cooling and ventilation account for just 3% of an average commercial building’s energy use according to comprehensive research from a BRE Report, which also shows heating and hot water account for a staggering 65% of energy consumption whilst producing annual carbon emissions of 10.4 Mt.*

These figures are supported by figures from the more recent Defra’s Market Transformation Programme (2006), which shows that providing heating and hot water accounts for over 50% of energy consumption in non-domestic buildings. Initial modelling from the Defra study of gas and oil-fired water heating boilers and warm air and radiant systems resulted in annual carbon emissions of 10.8 Mt.

As the BRE report shows (Fig. 1), there are other areas that can be addressed, such as lighting (23%) and catering (12%). Steps can be taken to modify this consumption, but if we do want to make a real difference to our building’s energy consumption — and reduce our annual fuel bills — we could do a lot worse than look at improving the energy efficiency of the heating and hot water supply.

This is where I believe heat pumps can make a significant difference, especially as technology emerges which allows excess heat to be used for more and more facilities — including the hot water supply.

Year-long tests at our Hatfield site, which we concluded last summer before the recent escalation in prices, have demonstrated once and for all that a properly commissioned, fully maintained and accurately controlled VRF heat-pump air-conditioning system is a more cost effective way of heating and cooling a building and produces less carbon emissions than the more traditional combination of a boiler in the basement and a chiller on the roof.

The tests involved a ground-source heat-pump VRF system and showed that it was 515% more efficient at heating than a boiler and 338% more efficient at heating and cooling than a typical chiller/boiler combination.

Ground source is not a viable option for everyone owing to capital outlay or space constraints, but the tests also show that the more readily available air-source heat pump systems also outshine traditional methods.

The reason is quite clear, as a brief explanation of the differences in the technologies shows.

Heating with a conventional gas boiler, 1 kWh of energy consumed by the boiler delivers less than 1 kWh of heat to a building. Modern commercial boilers generally have efficiency levels of 80 to 90% (gross) because some the energy is lost in the combustion process. The technology is near its limit in terms of capability as it cannot exceed 100%.

Fig. 1: Providing heating and hot water in commercial buildings accounts for over half of energy consumption (left) and half of carbon emissions (right). These charts are from the BRE and relate to the year 2000.

With a typical heat pump, 1 kWh of energy delivers a heat output in excess of 3 kWh — a 300 per cent increase in energy efficiency, and that performance is growing year on year as the technology develops.

This 300% efficiency is known in the air-conditioning industry as a co-efficient of performance (COP), and new models and advances in technology are already offering COPs of 4 to 5.

Yes of course we must take into account the inefficiencies of the national grid but with 300%+ versus (at best) 90% there is surely no contest. As gas prices rise and electricity production becomes greener (The Prime Minister has just announced new renewable targets), the benefits are set to grow year-on-year.

If there are still people who do not know the basics of a VRF system, it uses a refrigerant (ozone-friendly) circuit to transfer energy around a building and can therefore offset heating requirements with cooling from areas such as computer rooms.

However, even with the most balanced VRF system the building will not be in equilibrium all of the time — especially with the unpredictability of the British weather which, although generally temperate and ideal for heat pumps, can vary quite a lot within a single day.

This is where the VRF industry is now focusing to finding ways of using excess heat within the system to maximum effect.

One obvious target is domestic hot water, which focuses even more attention on the age-old method of heating our water and highlights the financial and environmental costs of traditional boilers.

Over the next few years we will see the introduction of Energy Performance Certificates, which, with the continued hikes in energy costs, will increase occupiers’ knowledge of, and demand for, more environmentally efficient property.

New legislation is already provoking a response from owners and occupiers, some of whom have appointed energy assessors to examine how much energy their building is using and where they can make savings.

The issues discussed here are all part of Mitsubishi Electric’s Green Gateway Initiative, which highlights how we can all reduce energy consumption in our built environment. .

Philip Ord is product marketing manager at Mitsubishi Electric.



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