By Paul Sands of Stokvis Energy Systems
The information super-highway, or Internet as we now refer to it, has revolutionised our lives, from the way we access data and daily news, to how we shop or book a holiday. It can even enable you, given the right control systems built into a dwelling, to switch on the heating before you get home using your mobile phone.
The fact is though, that most domestic heating systems are stuck somewhere in the second half of the 20th century, with millions of households still running standard efficiency, rather than high efficiency or condensing boilers.
The Climate Change Act and associated initiatives such as the Code for Sustainable Homes, with its stepped carbon reduction targets, enshrined in successive revisions for Approved Document L to the Building Regulations, are driving the uptake of both high efficiency heating systems and renewable technologies. Amongst the latter, biomass boilers, heat pumps and CHP (combined heat and power) units are proving increasingly attractive as we approach the 2016 deadline for building only near to zero carbon dwellings.
So while the ubiquitous ‘combi’ boiler remains the source of heat and domestic hot water (DHW) in homes as diverse as character cottages and high rise flats, M&E consultants and building specifiers are generally seeking far more advanced solutions to improve the SAP rating for their proposed properties.
The UK’s record regarding the adoption of district or ‘community’ heating systems is in many cases not a happy one, with estates relying on centralised boiler plant having suffered from leaks and heat loss through the distribution mains; or even infestations by pharaoh ants, living in the pipe lagging.
In contrast to the way our politicians perform, amongst heating engineers ‘lessons have been learned’ and there are now numerous examples in both the domestic and commercial spheres where centralised plant successfully provides heating and hot water across sites of varying scale. This renewed popularity is well founded because when correctly specified and installed they offer significant economic and practical benefits over individual heating systems, including the straightforward incorporation of solar thermal energy. Pivotal to these improvements has been the advent of sophisticated heat interface units or HIUs.
If we consider a tower block, a sheltered housing development or student cluster flats, installing individual boilers, or heat pumps, in every dwelling represents not just a very considerable capital cost, but also a continuing maintenance burden. Indeed across the affordable housing sector, gaining access to properties to carry out annual gas inspections is amongst the organisations’ most onerous responsibilities. Tenants resent what they see as an intrusion or have something to hide and RSLs resort to legal action or have to fit safety cut-out devices which will shut down the boiler if it isn’t serviced within a 12-13 month period.
With a communal or district system, properties are fed by low or medium temperature mains that will typically feature two or more high performance commercial boilers, located in a basement or purpose designed modular plant room. A cascade set up is also advantageous.
Gas no longer has to be taken into each dwelling while, without individual flues being required, the deadly risk of carbon monoxide along with the expense of maintaining alarms is avoided. Doing away with the vent terminals also tidies up the exterior appearance and negates the unsightly problem of pluming.
The very viable alternative is to install a heat interface unit, either within the dwelling – probably in the kitchen or a service cupboard – or in a dedicated cabinet opening onto the communal corridor. This way the heating engineer can gain access for servicing even if the tenant is away from home.
Water from the primary circuit passes through the HIU, featuring integral plate heat exchangers, which then transfers energy to the secondary circuit where it is used to generate space heating and domestic hot water. And the latter can be done directly rather than having to take up valuable space with a dedicated storage cylinder.
Whereas early district heating installations – such as the notorious St Anne’s scheme in Nottingham – offered residents very poor control over the heat delivered, and necessitated a flat rate charging arrangement, the modern HIU encompasses accurate heat metering. This means customers can be billed for exactly the amount of energy they have consumed, while the Internet allows this measurement to be carried out remotely, offering a further cost saving.
These advantages are a reality already, but as the designs for residential properties embrace the Government’s ambition for near to zero carbon living, the attributes of heat interface units become even more attractive.
Very low U-values for the building envelope have the effect of cutting the space heating requirements down to levels as low as 0.5-5kW; output levels where conventional combination boilers will struggle to operate properly. Constant on-off cycling can cause unnecessary wear, while producing sufficient domestic hot water is still likely to require a 30kW model to be used.
The combination of increased efficiency, practicality and safety with greatly reduced maintenance requirements makes a compelling argument in favour of heat interface units.