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installations but not for gas heating systems, until now. Gas central heating is traditionally oversized, but under the new regulations, boilers and heat emitters must be specified as closely as possible to calculated heat loss. While this change of approach might seem daunting
at first, it will ultimately lead to better specified systems and happier customers. Building services installers are making a positive contribution to the UK’s transition to a lower carbon future; something that our industry should definitely feel good about. Viva delivers gas and heat pump training from its
centre in Halifax
How do you calculate heat loss?
ENERGY EFFICIENCY
boilingpoint W
e should all now be aware of the introduction of the revised Approved Document L, Conservation of Fuel and
Power and the new requirements for space and hot water heating. Some of the key points are: From 15th June 2022 -
The heat loss calculations focus on fabric and ventilation losses. For fabric losses you need to consider the following: ¡ *U value = thermal conductivity of the fabric. ¡ A = area of the room (m²) ¡ ∆T = temperature difference between inside and outside To calculate the fabric loss, these three factors should be multiplied together. (U x A x ∆T). For ventilation losses, the following elements must be multiplied together: ¡ V = volume of the room or building (m³) ¡ N = air change rate per hour, dependent on the room type and age of the property ¡ ∆T – temperature difference between inside and outside ¡ 0.33 – the factor for the specific heat and density of air
Heat loss calculation support
Many of the boiler and heat pump manufacturers provide heat loss calculation tools, designed to take some of the headache away from installers. Daikin, for example, which we partner with at our Sustainable Homes Centre, have a number of tools for installers. These include the ‘Heating Solutions Navigator’, which brings together everything required to complete the design and selection of a heat pump system, including heat loss calculations, product specifications and schematics, energy labels and sound pressure information
¡ All space heating should be sized to take account of all of the building fabric and using an appropriate method, for example, the CIBSE Domestic Heating Design Guide. ¡ Gas combination boilers should be selected to modulate down to the typical heating load of the dwelling. ¡ New or fully replaced heating systems should be sized to operate effectively and in a manner that meets the heating needs of the dwelling, at a maximum flow temperature of 55°C or lower. ¡ Where it is not feasible to install a space heating system that can operate at 55°C temperature, the space heating system should be designed to the lowest design temperature possible that will still meet the heating needs of the dwelling. These new requirements have prompted members to ask how to meet hot water demands while providing space heating at a lower flow temperature and maintain efficiency of boiler with the fluctuating temperature demands and avoid the boiler switching on and off frequently due to the difference between the lower space heating and higher primary hot water temperatures - the answer lies in the control system. The typical control system we have been
installing up to now is an ‘on/off modulating system’. The ON/OFF period will be influenced by several factors, for example, weather compensation, hot water periods and demand along with internal room temperature etc. High load conditions would mean the boiler is on for longer periods with low load conditions maintaining temperatures meaning the boiler could be switching on and off for short periods.
This type of control has limitations and
may see ‘overshoot’ or rippling around the thermostat set point, where the room temperature is reached, but heat energy within the heating system will see additional heat
Heating demands vs hot water demands
coming into the room making it warmer than desired. The solution and alternative to this is the OpenTherm control system. OpenTherm is essentially a programmable language that was initially developed by Honeywell and has now been made freely available to all heating appliance and controls manufacturers to develop the system and its potential further through the OpenTherm Association. OpenTherm modulation operates on a similar principle to the ‘on/off modulation system’ but is achieved more directly by setting the desired water temperature from the boiler rather than by cycling it On and Off, this can often be at the gas valve. For ‘high load’ conditions a high water setpoint can be requested from the boiler. For example, during Hot Water periods. The water temperature being requested will then reduce over time as the stored hot water reaches the set point and switches back to maintaining the space heating requirements. The most important difference here is that the boiler will run for longer periods, but it will be producing water at lower temperatures, resulting in less energy being used and maximising the time spent in the higher efficiency condensing mode.
OpenTherm has the potential to significantly change the way we view, size and install heating and hot water systems with some developments even sensing hot water temperature at outlets etc. When considering this system, you will need to make sure the boiler, controls and components are all OpenTherm compatible and have the OpenTherm logo. Already most boiler and controls manufacturers have OpenTherm appliances or branded appliances that are compatible. For more information on the system or organisations with compatible products go to
www.opentherm.eu
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October 2022 33
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