Water heating in commercial buildings
With 2016 just over two years away, the specification of energy efficient products is gaining in importance, especially when it comes to the generation of domestic hot water. Peter Gammon, Technical Manager at MHS Boilers, looks at the best options available.
In July this year, the government dropped plans to implement changes to Part L of the Building Regulations, heightening fears that further delay will undermine the push towards the 2016 carbon reduction goals. The requirements laid out in Part L are seen as critical to further improving the energy efficiency of non-domestic buildings, as well as a key part of the government’s commitment to cut UK emissions overall.
Despite the expected arrival date now being April 2014, there is unlikely to be any let up in improving and utilising the latest technology for heating plant – and, in particular, optimising water heating systems and their capabilities to improve energy efficiencies. Indeed, the amended regulations for non-domestic buildings are set to strengthen the CO2 targets, with a 9% improvement on 2010 standards. These new regulations are also set to coincide with the introduction of the domestic Renewable Heat Incentive (RHI) tariffs, which will further increase the incorporation of renewable products in residential buildings.
So, with impending changes to Building Regulations and renewable incentives, what are the best options for consultants when specifying bulk hot water delivery? The first consideration is the level of demand for hot water, and this can be split into three main categories; continuous demand (such as an industrial process); intermittent peak (hotels or schools) and short heavy peaks, which often occur in sports clubs and leisure centres.
One tried and tested method for bulk hot water delivery, which is ideal for continuous and intermittent peaks, is the latest range of indirect gas-fired instantaneous hot water generators. These generators deliver extremely high volumes of domestic hot water and, thanks to their integral condensing boilers, allow for consistently high efficiencies. The other benefit of using such products is that not only are they capable of providing volume hot water for peaks of usage, the power to storage ratio is such that they recover very quickly and respond almost instantaneously to hot water usage.
However, there is a note of caution when specifying these types of products – scaling. At typical hot water storage temperatures there is a high risk of scale fouling, especially in units that heat the tap water directly through primary heat exchangers. Even a very thin layer of scale will cause a reduction in the unit’s performance, and have significant impact on the lifetime efficiencies. Potentially this problem can lead to heat exchanger failure and, consequently, the best approach is to use an indirect unit – preferably with a stainless steel heat exchanger, such as the Thision WH from MHS Boilers.
The combination of renewable technology and domestic hot water (DHW) should also be considered, provided it’s specified and installed correctly. Solar thermal is often a specifier’s first choice for integration into a building’s heating system to provide DHW. There are plenty of statistics on the contribution of DHW from solar thermal systems, but, in general, a well designed solar thermal system can provide up to 50% of the DHW needs of a building. It is also a relatively cost effective way to incorporate a renewable source of energy and, considering the commercial RHI tariffs and forthcoming domestic equivalent, can be an attractive option in the long term.
In a commercial context, solar thermal works particularly well in buildings with a reasonably high and regular demand for hot water because, with solar thermal, any heat generated needs to be used or stored.
A good example of effectively integrating solar thermal can be seen at the new JW3 Jewish Community Centre Finchley, London. This multipurpose building houses a nursery, screening room, restaurant, bar and community spaces, as well as a 10-storey residential block, which comprises 14 two-bedroom apartments. By specifying 60sqm of evacuated tube solar collectors on the roof of the building, the system is capable of supplying an impressive proportion of the DHW requirements, while significantly reducing the utility costs of both buildings.
The installation provided a solar fraction of 50% for the apartment block, displacing 5,371 kg CO2 per year and 8,061 kWh of electricity. At the same time, the main community building saves 816 cubic metres of gas and 1,725 kg CO2, with a solar fraction of 35% – proving that when specified correctly, solar systems can be particularly effective.
Given seasonal variances in the amount of solar irradiation, the performance of a solar thermal hot water system is averaged over a year. Consequently, any hot water system designed to work in conjunction with a solar thermal source must be independently capable of performing to the needs of the building without any solar input. This allows for the lower solar energy availability in winter months and overcast days that often occur in the UK.
The essential information when planning a solar thermal system is the volume of hot water required by the building on a daily basis. Once known, specifiers can quickly ascertain the number of solar collectors needed and the capacity for DHW storage. Accuracy is particularly important at this calculation stage, as a solar thermal system can very easily end up stagnating if specified incorrectly and oversized. For example, in the summer, energy is likely to be pouring into the collectors and, by mid to late morning, the storage cylinder is often up to temperature. Unless this water is used, the array of collectors will likely reach their maximum working temperature, effectively closing it down for the rest of the day. Only once the sunlight has diminished will the collector fluid cool and condense, allowing the system to return to heating mode once again.
Of course, there is never one product or system to suit the needs of every building. However, with careful planning and real consideration of the factors discussed, it’s easy to ensure that DHW can be delivered effectively, while keeping energy usage to a minimum. Specifiers and consultants should look to established manufacturers when targeting the impending tightening of Building Regulations. They have a wealth of knowledge and expertise on hand, so specifiers, and those responsible for product and system selection, would be well advised to seek their help from the outset. After all, water heating products are continually evolving, so why settle for anything less than the latest available technology?