Modern Building Services

MODERN BUILDING SERVICES FEBRUARY 2023 19 FEATURE HEATING A clear benefit of this arrangement is that it isolates the LZC heated water from the potable DHW supply, so there is no risk of legionella. This means the water in the mild steel vessel does not require daily pasteurisation, thereby reducing energy consumption. Other anti- Legionella measures for stored DHWwill, of course, need to continue as usual. Even if the hot water in the mild steel vessel only reaches 35°C this will help to reduce the energy consumption of the other heat sources. As long as the stored water is at least 6°C above the temperature of the incoming mains water, there is an opportunity to achieve a worthwhile heat transfer. If high storage volumes are required, several non-potable thermal storage vessels can be piped in series, using diverting valves to circulate the water and enhance stratification. This allows other LZC heat sources, such as biomass boilers, to be fully integrated within the scheme and support the pre-heating strategy. When demand for DHW and space heating is high and demand tends to be in peaks and troughs, there may also be a need for fast response heating at peak times. Typically, this will be met by high efficiency gas-fired condensing boilers, combined with effective controls that ensure the use of such heat sources is minimised. If specifying new boilers, it’s also worth ensuring they are hydrogen ready able to use up to 20% hydrogen blended with natural gas at the moment, and easily converted to 100% hydrogen in the future. Using a pre-heating design also makes it very straightforward to retrofit LZC technologies to an existing heating system, thereby enhancing the business case for investing a low carbon solution. CHP and heat networks With the introduction of small- scale combined heat and power (CHP) to the market, many hospitality and leisure venues are now able to take advantage of this technology as part of their heating mix. Typically, where CHP is used it will be part of a mixed heating system that also incorporates other heat sources. A familiar configuration is to use gas-fired CHP alongside gas-fired condensing boilers. Here, the CHP will usually be used to meet base heat loads with the gas boilers providing a top-up at times of peak demand. This arrangement needs to maximise the run times of the CHP, so it’s important that the base heat load is sufficient for the CHP to run for at least three hours each time it fires. Here, the inclusion of thermal storage capacity can be useful as it enables the CHP to keep running once the building’s immediate heat loads have been satisfied, thereby increasing the amount of onsite power generation. With such onsite generation using CHP as part of the heating mix, there will also be the generation of electrical power for use in the facility or for export to the grid. It’s therefore important that CHP units are fully compliant with the Engineering Recommendation (EREC) G99 standard. This standard ensures harmonised network standards (Requirements for Generators) are incorporated into Great Britain’s distribution and grid codes for CHP and other power generators with capacities between 0.8kW and 1MW. Taking and maintaining control The situations described above are just some examples of how high demand for DHW can be met with a mix of heat sources. In all such cases, efficient control is essential. Experience has shown that trying to control multiple heat sources with different controllers is extremely difficult and will usually compromise overall performance. Consequently, modern controllers now need a wider remit insofar as they can take effective control of a range of heat sources, with the ability to handle single units or operate cascades of heat sources. For example, it is now possible to install a single controller that will control CHP, boilers, heat pumps, and solar thermal and other heat sources that may become available in the future. Connectivity through the internet is now also an expectation of many building operators, so it should be possible to remotely monitor the system from a computer, tablet or smartphone, with alerts for routine or reactive maintenance. Similarly, integration with a building management system using OPC UA, ModBus or KNX interfaces, along with smart grid readiness, are rapidly becoming de rigueur. Equally, controllers need to make it easy to re-commission the system to reflect changing DHW and space heating loads through the life of the building; perhaps due to changes in usage or improvements to the thermal performance of the building fabric. In all these cases the control strategy needs to be updated accordingly and this is a far more straightforward process when using a control system that is easy to re-configure and re-commission. Summary Whenmeeting the demands of buildings that have higher heat loads for DHWthan space heating, delivering themost efficient solution requires a combination of optimum systemdesign and efficient control. In thisway, the building operator enjoys the environmental and cost advantages of lowcarbon heat without compromising on the service provided to the building’s users. More information can be found at www.hoval.co.uk