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The viewpoint used to decide items is a balance between the outlay cost and the running costs. This system will not be the cheapest way to produce heating and hot water nor the most expensive installation system but a balance related to the existing equipment and personal requirements. BEST ADVICE: Read the manual of the product you are proposing to use BEFORE you buy, especially regarding the installation and check that it will work for you. Choosing the ASHP: The size of the ASHP was determined by the heat loss calculated and the peak heat demand when the outside temperature is -8C. This resulted in the requirement of a small ASHP. We did not want an all singing all dancing system, but one that would combine with the existing central heating radiators/hot water tank and MVHR. An air to water ASHP was chosen to be able to use the existing central heating radiators already installed. The radiators are too small to produce enough heat at the lower running temperature of an ASHP so water coils are being installed in the MVHR system. The other alternative would have been to replace the radiators with larger ones as the existing ones are almost all single panel which could be replaced with double panel to increase the heat output. This option is going to be held in reserve depending on the effectiveness of the water coils in the MVHR ducts. The ASHP was chosen for it minimum working temperature of -20C and the fact that it had an inverter. An inverter heat pump uses a variable speed compressor which modulates its output increasing or decreasing its speed to match exactly the heat demand requirements of the building as the outdoor air temperature changes. This makes for a more efficient output. Because the bungalow is on the edge of an estate we wanted have a low noise unit. The unit installed is listed as 46 and 60db. I think that means 46db when running at lowest and 60db when flat out. (I'm sure someone will tell me). With the distance from walls and other properties this is well within MCS requirements. Because the bungalow suffered from strong solar gain in the summer the choice was made to install an ASHP with cooling. ASHP - planning, MCS: In order to avoid requiring planning permission the decision was taken to install the ASHP under the permitted development rules. The only position where the ASHP unit could be situated within the rules was on the flat roof. Because the flat roof has 200mm of PIR and the ASHP unit is about 88kgs concern has been raised that the vibrating motion may erode the PIR over time. The decision was taken to install and monitor the out come. The positioning gives an open run of air to the unit, but far enough from neighbours to hopefully avoid problems. Its. not perfect because during the summer it is exposed to the full sun. We hope to mitigate this when cooling the building by using the PV energy to run the ASHP. The theory being: Summer=hotter sun=more electricity produced= more power to produce cooling using the ASHP. ASHP pipework: The shorter the pipework between the ASHP and the thermal envelope of the building the more efficient. The greater the pipe insulation the more efficient. The shorter the pipework between the ASHP and the hot water tank/ heating system the more efficient, especially to/from the hot water tank as the water temperature is usually higher. ASHP connections: The pipework required is 28mm for this ASHP all the way round through the hot water tank, through the buffer tank and back to the ASHP. We used 25mm thick insulation. Two flexi hoses were used at the ASHP end with two 28mm isolating valves. The power cable used was 6mm twin and earth. The cable size is related to the possible voltage loss not just the power required! Apparently the ASHP is sensitive to voltage loss. To be honest I think 4mm could have been used but there was a roll of 6mm purchased for the PV with enough excess, so this was used. A suitable fuse was required which needed to be a MCB or RCBO Type C 20amp with this ASHP. A RCBO was installed. The control of the ASHP is via a Carel LCD "user-friendly" interface Controller and various electrical links. (More later as this develops...) The 3 port valve is a 3 Port Diverter Valve not a 3 port mid-position valve. The mid-position would allow water from the ASHP to go both to hot water and heating at the same time. However the temperature of the water flowing to heat the hot water tank is expected to be different to the temperature of the water flowing to the heating/cooling. The water side of the system will require antifreeze. so the volume of the water will need to be calculated... Please let me know what else I have forgotten...