Matching renewable energy to application
With the wide choice of renewable technologies available, what is best for a particular building? Kingspan Environmental’s Stephen Kelly offers helpful advice.
For consulting engineers, the need to install renewable technology and reduce CO2 emissions is now a standard requirement for new UK buildings to meet the latest Part L of the Building Regulations.
The decision as to which technology to install usually includes a review of both the building’s budget and a calculation of the potential CO2 savings to determine which solution (solar panels, air-source heat pumps etc.) could be installed to achieve the required environmental standard. Once a viable solution has been identified, the designs are passed on to the manufacturer’s engineering team to size and specify a system.
While the process may be fairly well established, there are a number of variables that should be accounted for because of the impact they could have on the benefits provided by the technology in terms of both payback and its effectiveness.
Some renewable technologies, for example, are better suited than others for particular buildings. The suitability is largely determined by factors such as the building’s use, occupancy, location and requirement for energy.
There are also other considerations around individual buildings that might unfortunately mean the best solution on paper doesn’t then work in practice. The property’s size, style, or aspect might rule out the installation of one technology, but support another.
Getting it right first time can save a considerable amount of time and design cost. More importantly, the right solution means the system efficiency and payback time will be optimised.
Bringing in the expertise and experience of a manufacturer’s engineering team to advise on solutions before designs are finalised is recommended; it will help save a great deal of money, time and effort.
But there are also some general principles worth bearing in mind when considering which renewables technology will suit which building.
Solar thermal, which uses the Sun’s energy to heat water, works particularly well for buildings with a heavy, constant requirement for hot water — such as a swimming pool, or a care home. It works well in domestic settings, too, where there is typically a steady demand for hot water, supplying up to 70% of a household’s requirements. A useful tip is that in a domestic setting occupancy levels are more important than the size of the house when sizing a system.
Other buildings might have a high demand for hot water but not a constant requirement. An example is university accommodation, and engineers must carefully calculate annual load profile when sizing a solar thermal system, understanding that during the hot summer months occupancy levels will drop substantially, as will hot-water demand. If such variable occupancy is not factored in, not only will the solar thermal system be larger and more expensive than it needs to be, but because it will be oversized, it also runs the risk of over-heating.
For space heating and hot water, biomass boilers are commonly specified — not least because they are an easy switch from an oil boiler. However, the need for regular access to a building can mean that a biomass boiler is not the best solution. For example, deliveries of pellets by articulated lorry may not be viable if a building is in a remote setting, and/or pellet storage may be problematic in some situations because of the size of the silo or hopper required.
More recently, air-source heat pumps have become increasingly popular for space heating in both commercial and domestic applications. Not only can they extract heat from air all year round, but they are also extremely powerful — with the technology developing further all the time. Air-source heat pumps are particularly suited to underfloor heating systems with relatively low flow and return temperatures and are very easy to install, without any fuel storage requirements.
Small wind turbines, such as our KW3 and KW6 turbines, offer a year-round source of energy for some developments. Wind speed is particularly important in determining their potential effectiveness; usually a minimum of 5 m/s is required, but the power output can be very impressive. A single KW6 turbine can produce yields ranging from 9 MWh to over 25 MWh a year, depending on wind speeds. This, along with the need for exposed sites to reduce air turbulence, means they are popular with the agricultural community.
Of course, high wind speeds can be just as much of an issue, such that some wind turbines have to be shut down. We would recommend choosing a turbine, like the KW3 or KW6, that offers continuous operation regardless of wind speed.
Renewables technologies can also be combined to great effect. Armstrong Point, a business park in Wigan, combines a wide range of renewables, including air-source heat pumps, solar thermal and wind. Not only is the carbon footprint of the park vastly reduced, but for the first time in the UK, tenants will not pay a penny for the energy they use.
Whatever choice of technology is finally made, correctly sized, we calculate that our renewables technology could pay back within six to seven years if sited, designed and sized to optimise efficiency.
Stephen Kelly is specification design manager with Kingspan Environmental.
A steady demand for hot water from, for example, care homes and swimming pools (this is Bristol Lido) are good applications for solar thermal to generate hot water.