Commercial heating
Designing to meet DHW demands
T
here are many building types that have higher demands for domestic hot water (DHW) than typical commercial buildings, such as hospitality and leisure venues. In these cases, the right control of the right heating technologies can help to ensure that low carbon heating technologies such as solar thermal and combined heat and power (CHP) play a key role in meeting DHW demand. For example, inclusion of solar thermal in such a
system often requires a ‘re-think’ of traditional strategies to take full advantage of this low carbon opportunity. Historically, many mixed heating systems have been designed to use renewables as a ‘top up’ source to traditional heating technologies, often imposing limitations on the use of the renewable element. A better solution is to use the solar energy as the pre-heat source for DHW
and then supplement from other heat sources. In this arrangement, a mild steel vessel is also incorporated, solely for storing
the water heated by the solar panels and pre-heating the DHW via a plate heat exchanger. This isolates the solar-heated water from the potable DHW supply so that there is no risk of Legionella and also means the water in the mild steel vessel does not require energy-consuming daily pasteurisation. Other anti- Legionella measures for stored DHW will, of course, need to continue as usual. Where 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 will promote solar gain and also allow other renewable heat sources, such as biomass boilers or heat pumps, to be fully integrated and support the solar thermal system. Moreover, this arrangement makes use of the solar irradiation that is available
even on cloudy days. If the hot water in the mild steel vessel only reaches 35°C this will help to reduce the energy consumption of other heat sources. Worthwhile heat transfer can be achieved as long as the stored water is at least 6°C above the temperature of the incoming mains water. When solar energy is plentiful, the temperature of the water can be allowed to
reach temperatures up to 90°C before the system pumps are switched off, without any risk of scalding. Also, using solar energy to pre-heat DHW makes retrofitting solar panels straightforward and cost-effective.
CHP and heat networks With the availability of small-scale CHP, many hospitality and leisure venues are now able to use this technology as part of their heating mix. Typically, where CHP
November 2019 Taking and maintaining control
In all cases, of course, efficient control is essential. Experience has shown that trying to control the multiple heat sources with different controllers is extremely difficult and often compromises overall performance. Consequently, modern controllers need to take effective control of a range of
heat sources, with the ability to handle single units or operate cascades. For example, it is now possible to install a single controller that will control CHP, boilers, heat pumps, 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 that the system can be monitored remotely 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 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
Where a building has higher heat loads for DHW than space heating, efficient control and optimum design are essential. This approach ensures the building operator gets the environmental and cost advantages of low carbon heat without compromising on the service provided to the building’s users.
www.heatingandventilating.net
Ian Dagley, general manager of Hoval
When designing systems for applications where there is a high demand for domestic hot water, it’s important to optimise use of low carbon heating technologies, says Ian Dagley, general manager of Hoval
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, with the CHP meeting base heat loads high efficiency 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, again, inclusion of thermal storage capacity enables the CHP to keep running once the building’s immediate heat loads have been satisfied, thereby increasing the amount of onsite power generation.
www.heatingandventilating.net
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48
