FEATURE
HEATING
THE ESTIMATION GAME Providing estimated running costs for any heating system, including electric, can be a tricky affair. Shaun Hurworth at Glen Dimplex Heating & Ventilation, outlines just what makes estimates so difficult, and explains why exact quotations may be little more than guesswork.
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s a contractor, it can be frustrating to be asked to supply expected running costs for any heating system. Not only does this raise a raft of follow-up questions relating to factors such as expected usage, fuel costs and building efficiency, but it also hints towards an over-reliance on price that might prevent a customer from choosing the most appropriate system for them. The problem is that providing running costs involves a series of calculations based on data that it is impossible to know from a pre-purchase perspective. As a result, any estimate provided may not only be inaccurate – it could be downright misleading for the decision-maker.
Unhelpful or unwise? Admittedly, there are some manufacturers who will supply an estimate of some kind on request, and it is true that producing a running cost value alongside a specification isn’t entirely impossible; it does, however, rely on some fairly large generalisations. The best way to illustrate this is probably to describe how one would go about forming a running cost estimate in the first place. A heating system is designed to bring a space up to the required temperature, and maintain that temperature by replacing any energy which is lost from the space. As such, the running costs for the system come from a combination of the difference between the internal and external temperatures (referred to as ΔT), and the U-Values of the insulators between the spaces. In other words, how much energy
“Electric heating is 100% efficient at the point of use, meaning that every kWh that the heating system draws through the meter becomes heat in the space.”
passes through the insulation from the heated space to the unheated one. Electric heating is 100% efficient at the point of use, meaning that every kWh that the heating system draws through the meter becomes heat in the space. Because Lot 20 legislation introduced minimum compliance levels for the accuracy of thermostats, a heating system will draw the precise amount of energy it needs to keep the room at the set temperature, and this equates exactly to the amount of energy that is lost to the outside space. Let’s apply this to a real-life scenario. If a building has a 10kWh heat-loss at 10ºC ΔT (i.e. it’s 20ºC inside, 10ºC outside, and 10kWh leak through the walls, windows, doors and ceiling) in a set period of time, then any electric heating system will have to draw 10kWh through the meter to keep the space at the temperature of 20ºC. Given that the standard tariff for electricity is currently at 15.4p and 7.5p for off-peak, according to confusedaboutenergy.co.uk, May 2018, if you replace this 10kWh of lost energy using direct-acting heaters then the running cost would be 15.4p/kWh x 10kWh = £1.54 per hour. However, if you were to replace that lost energy with heat stored from the offpeak tariff, then that cost reduces to 75p.
26 | August 2018
Heating – Dimplex.indd 26
26/07/2018 14:24