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Hi, does anyone know (for certain) whether retro-fitting battery storage (AC coupled) to an existing Solar PV Installation that benefits from the old FIT requires the installer of the battery to be MCS Certified so as not to compromise the FIT payments? ...or can anyone point me to where it is confirmed either way?
Hi, perhaps someone with more experience than me can help. My gas usage for the last year is around half that suggest by a recent MCS ASHP survey. I really don't want to pay for and live with a double height HP unit if its not needed, but don't want to undersize either. I live in 160m2, 4 storey mid terrace house in Bristol. C 1870 Extended to the rear and loft so half of the exposed walls are essentially new build levels of insulation and air tightness. Floors are fairly well insulated. Mixture of rads and wet UFH. Fully double glazed, half the exposed walls are 300 and 400mm uninsulated solid brick/ stone. as mentioned we are looking to install an ASHP. my measure gas usage does not match the ASHP installers calcs. My figures for heat loss at at -2c are 4- 5kw and theirs come out at ~9kw. (i calculated this from measuring gas usage over the year, used degree days to establish a heat loss per degree difference in/out. then see what it gives at -2c ) Annual usage is equally off. Our gas usage was 9000kwh for the year and the calcs suggest 19000kwh. (no calculation by me on these numbers) For refence that gives a measured value of 56kwh/m2 vs calculated 119kwh/m2 Finally I ran our combi at 40 degree flow for the past winter (coolest average day was 2c ) and maintained 20degree internal temp fine. but the calculation suggest the radiators would only keep interior temp of 20c with flow of 55c and outside temp fo 3 degrees. which would be far from ideal. Do calculator tend to over estimate? I have worked hard to reduce drafts, perhaps the clacs are based on an assumption for an old drafty house ? any advice on if my measured figures seem plausible? The renovation has been done well but not to enerPHit. opinions on whether oversizing or under sizing is the better option welcome. Our primary aim of ASHP is CO2e reduction not financial. Thanks in advance. Joe
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...