hot_water_cylinder

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Work out the daily hot water demand of a dwelling and the size of cylinder a heat pump needs, using the formula in MIS 3005-D 3.5.2 and the BS 6700 guidance reproduced in MGD 007. The demand is 45 litres a day for each of N, where N is the greater of the number of bedrooms plus one and the number of people actually living there. For a new build, where occupancy is unknown, the bedroom count is used. The cylinder does not have to hold a whole day's demand, because it reheats as it empties. What it must cover is the largest draw-off before the heat pump catches up, which is why a larger heat pump needs a smaller cylinder: reheat time is volume times temperature rise, divided by 14.3 times the kW. The result gives the BS 6700 minimum, a recommended size rounded to a volume cylinders are made in, and the reheat time. Note that cylinder volume is not the whole story: a heat pump cylinder needs a much larger coil than a boiler cylinder, because the water arrives cooler and there is less temperature difference to drive heat across the surface. Method from MIS 3005-D. These calculators follow the published MCS methods, for understanding a system and checking a quotation. Anything that gets installed still needs a design and a site survey from a certified installer.