Marriage of LZC technologies
With commercial properties requiring 10 to 15% of their energy to be derived from some form of LZC or renewable energy solution, Yan Evans explores some options.
Despite views on the economic climate here in the UK, the interest and uptake of low- and zero-carbon technologies appears to be continuing in both the communally heated residential schemes and the commercial sector. However, the application of technologies, such as, solar thermal solutions, ground and air source heat pumps and combined heat and power (CHP) are somewhat different for domestic and commercial installations.
In the domestic sector it is very likely that renewable technology such as ground-source or air-source heat pumps will replace the conventional fossil-fuelled appliance due to investment and space limitations.
However, for commercial applications, we are witnessing the use of a combination of conventional boilers and water heaters working alongside LZC solutions to deliver a low-carbon plant room. This trend is currently being driven predominantly by local-authority planning consent. End users, architects, design engineers and contractors are all striving to design and build properties where 10 to 15% of the energy is derived from some form of low-carbon or renewable solution. In some cases this could mean several tens of thousands of kilowatt hours a year being required from solutions such as solar hot water, heat pumps, biomass boilers, photovoltaics and CHP — or a combination of these.
With products and solutions that generate heat there is a much greater chance of operational conflict due to the available heat load, whether space heating or hot water. The exception may perhaps be properties connected to a district-heating scheme.
For example, let us consider solar thermal and CHP on a given site.
To maximise the economic and environmental benefits of CHP, it is necessary to select the unit on the basis of the base thermal load to maximise the annual running hours. CHP units are heat-led devices that will not operate if there is insufficient thermal load. For many new-build properties, the base thermal load during the Summer will be limited to hot water, with little or no demand for space heating to sustain CHP unit operation.
Solar thermal collectors deliver the maximum energy during Summer when there are high levels of available solar irradiation, long daylight hours and higher ambient air temperatures.
Solar thermal solutions are often sized and designed for the daily hot water demand to maximise annual average solar fraction (the percentage of hot-water demand satisfied by solar energy). This sizing strategy would deliver a solar fraction of 30 to 40% for a commercial property. The solar fraction during the Winter could be as low as 15 to 20% and 100% in the Summer, with solar energy satisfying the daily hot water demand. There would be no need for any primary heating appliances such as boilers or direct-fired water heaters during the Summer, leading to significant reductions in fuel consumption and corresponding carbon emissions.
However, if solar energy is satisfying the daily hot-water demand, there is no hot-water load to offer the CHP unit during the Summer, when there is also no heating load. In this scenario, the solar thermal system would hold off the CHP unit, reducing the annual operating hours and having implications on the economic and environmental benefits of the installation. As CHP displaces electricity with a higher carbon intensity compared with natural gas (0.43 kgCO2/kWh for grid-supplied electricity versus 0.193 kgCO2/kWh for natural gas), the operation of the appliance offering the greater carbon dioxide benefit is hindered.
The combination of solar thermal and CHP can work in the correct application and with suitable selected equipment outputs. If there is sufficient base thermal load to support the operation of the CHP unit and the solar collector array during the Summer, then the marriage of these two technologies can deliver significant carbon-dioxide reductions.
Another potentially ultra-low carbon solution is the use of ground-source heat pumps alongside CHP. These technologies can work extremely well together. Both are heat sources and, provided there is sufficient base thermal load to support the operation of both appliances, there is no reason why they cannot work in harmony. In fact, the electricity generated by the CHP unit could be used to power the heat pump under normal operating conditions, with a significant impact on the carbon footprint of the solution. The CHP unit would effectively ‘de-carbonising’ the heat pump.
There is the potential to deliver a plant room design that offers significant reductions in carbon-dioxide emissions and an hydraulic schematic that includes conventional fossil-fuelled appliances working alongside and in harmony with LZC technologies.
Equipment selection is not the only issue that needs careful consideration. The appropriate control of the operation and interface of a variety of heat sources needs to be carefully thought out. This is the critical success factor to ensure that carbon-dioxide reductions are maximised with no compromise in the provision of space heating and hot water.
The more complex the mechanical and electrical services become on a project through the application of multiple heat sources, the greater is the pressure applied to the suppliers of conventional and LZC technologies to have a more input into the system design.
At Andrews Water Heaters and Potterton Commercial we are experiencing an increase in requests for us to have a higher level of input into the application engineering, and we actively support this trend.
To ensure such projects are a success, we believe that the equipment supplier has an important contribution to make and should be regarded as part of the project team. We are no longer simply an equipment supplier, but see ourselves as a solutions provider and encourage early participation in the plant room design.
Yan Evans is technical director of Baxi Commercial Division.
