40 HPM 1216

HPM-12-DEC-2016

40 T R A I N I N G & TECHNICAL Avoiding being in hot water HPM’s technical expert, John Love, shares his experience of one particular hot Iwas recently asked to look at a domestic hot water (DHW) problem on a project which was completed earlier in the year. The project involved a new two-storey rear extension plus loft conversion to give a bed sitting room and shower room. The property originally had a vented storage type DHW system with cold water tank in the loft. Because of the loft conversion there was no room for the cold water tank and so a combi boiler had been installed in the new ground floor utility room which supplied hot water to the kitchen, utility room, existing re-furbished bathroom with bath and shower, and the new loft extension shower room. Teenage children The house is occupied by two adults and two teenage children and the contractor was told that an adequate hot water supply to enable two showers, or a bath and one shower, at the same time was essential. However, the client had found that the combi boiler simply could not cope with this requirement and they had to wait a very long time for hot water to reach the attic shower room, by which time it was noticeably cooler. The problem was further exacerbated by the installation of high flow rate shower heads, which would not be allowed under Building Regulations in a new property. The contractor had originally wanted to install an unvented DHW cylinder but the client did not want storage space taken up by a cylinder, so the contractor allowed himself to be pushed into installing a combi. Bad mistake This was a bad mistake as he should have insisted on installing an unvented cylinder, or at least given the client a written disclaimer in respect of any failure to meet its specified hot water requirements from the combi. I was asked to propose a solution to the problem and I had to tell the client that it should have accepted the contractor's original proposal for the installation of an unvented DHW system. The client maintained that the contractor did not advise it of the implications of using a combi, and it was not happy with the prospect of the further costs to remedy the situation, but that is a matter which will have to be resolved between both parties. Since the client had a brand new combi installed, I suggested a hybrid combi/storage DHW system with the combi boiler, which was installed in the new utility room, providing an instantaneous hot water supply to the sinks in the kitchen, utility room and cloakroom – all quite short pipe runs. A new high recovery rate horizontal unvented DHW cylinder could then be installed in one of the attic perimeter roof voids, which was alongside the shower room, to supply the shower room and the first floor bathroom, which was fortunately almost directly below the shower room. The structural engineer confirmed that there was no problem with the additional weight of the cylinder in the attic. The space heating side of the boiler was modified so that it was piped up as you would for a normal storage DHW system - the heating flow from the boiler going to a three-port valve (or two two-port if you prefer) which then directs the water to the space heating circuit or the hot water cylinder, as required. Disconnected and re-supplied The DHW supply from the combi. to the first and second floors was disconnected and re-supplied from the new cylinder, so the only problem was the routing of a new 22 mains cold water supply and 22 primary heating flow and return up to the new cylinder. To avoid to much disturbance to the building, these pipes had to follow quite a circuitous route, but the heating pipes were highly insulated to minimise heat loss. With the high recovery cylinder, which only needs to be heated for relatively short periods morning and evening, when there is a demand at the bathroom or shower room, the long primary piping run heat loss was acceptable. Pressure reducing valve The normal safety controls were provided on the mains cold water supply to the cylinder, except that the pressure reducing valve had to be installed at ground floor level so as to cover the cold water supplies which were all connected from the ground floor. In fact, this hybrid combi/storage system is one that I have utilised several times in the past, where the bathrooms/shower rooms are remote from the kitchen and utility rooms, because it avoids long draw-off legs to the first/second floors and avoids wasteful heat loss from a large quantity of hot water stored throughout the day. John K Love CEng, FCIBSE., FIPHE., FIDHE., MInstR., FConsE water problem that he encountered recently For your chance to win this prize, simply answer A or B in response to this question and fill in the form at the back of the magazine: What is lost because of a system failure? A: Money and time B: Sweat and tears System failures can be a costly and time consuming affair, but with regular maintenance, systems can be kept working at their optimum condition for longer. With Spirotech’s innovate solutions, you can be sure you are armed with the right tools for any job. The Spirotech bundle provides you with everything you need to minimise the risk of future failure and malfunctions. You’ll receive: a SpiroPlus Pack, with a SpiroTrap MB3 dirt separator, SpiroPlus Power Cleaner and Protector, SpiroVent RV2 deaerator, flush connector, Snickers polo shirt and cap. Answer A 134 REMEMBER: enter all 12 competitions, and you could win the grand prize - the lot! www.hpmmag.com December 2016 Festive Giveaway 8prize Prize 8 Spirotech bundle Answer B 135


HPM-12-DEC-2016
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