HantsBob

Thanks for taking the time to respond. I didn't explain carefully enough about the Sunamp Thermino. It is described as a heat battery but it does not store electrical energy. It stores energy in the form of heat, so similar in function to a DHW cylinder. However, you have answered a question that had occurred to me, but which I had not yet asked, regarding placement of electrical home batteries. That may be next year's project. As regards placing the hot water tank in the loft, it is certainly not my ideal solution but given our space contraints it is a potential solution that needs to be understood. To this end, can anyone explain the, presumably, standard conditions under which heat loss is stated. For example, I've just found the specification for a cylinder that states heat loss as 2.16 kWh/24 hrs. I assume the critical information is the temperature difference assumed between the hot water and the air outside the cylinder. But what difference will have been assumed in producing this heat loss figure. Also, would I be correct in thinking that if the temperature difference were, say, 20% greater that the heat loss would also be 20% greater? Thanks also to the others that have responded. I am aware that ideally the house should be well insulated and air-tight. We are doing some work in this area, perhaps we should consider more. However, looking at gas usage over a few years gives a fairly good idea how much heat energy we need to keep the house warm. Given suitably upgraded radiators and pipework a ASHP should have no difficulty in pumping a similar amount of energy in.

Thanks for the incredibly quick replies, even those that can't answer the questions😀. To answer a few of the points raised: Energy audit: I have done my own detailed heat loss calculation. Before accepting any quote for the heat pump etc. I'll be looking in detail at the installer's own heat loss calculation and proposed solution and ensuring as far as possible that I understand what they are proposing and why it should work. The questions I'm raising on this forum are part of the process of making sure that I'm as well prepared as possible for assessing proposals. Current hot water situation: Yes we almost always have enough hot water - very occasionally when visitors stay it starts to run noticeably cooler. The hot water is currently turned on (ie the gas boiler will heat the water whenever the thermostat calls for heat) from before we get up until about the time we go to bed. In future I'd hope to be able to make sensible use of time of day electricity tariffs and excess PV production. CoP: I had thought that the CoP was basically a function of flow temperature and ambient temperature. I'm happy to be corrected. Additional work: I expect much of the central heating pipework and the majority of the radiators to be replaced. Hot water temperature: good point that storing hot water at a lower temperature implies requiring a larger tank.

Hello. Thought I ought to admit straight away that I've never self-built, nor do I have any intention of self-building in future. Also, my currently proposed renovation is somewhat smaller in scope than many on this forum. I am hoping to replace my current gas-boiler driven central heating and hot water system with an ASHP later this year and have been seeking quotes for this work. Having googled many questions that have been perplexing me I keep finding useful information on this forum, hence my decision to join so that I can ask specific questions for which I've been unable to find answers. So, if I'm not immediately evicted from the forum for fraudulent application I'd like to start off with some points about the Domestic Hot Water side of the problem. My current hot water cylinder is over 40 years old, is relatively small and is probably heavily scaled internally. I'm certain it needs replacing. It may be possible, with difficulty, to fit a slimline modern cylinder into the airing cupboard where the current cylinder resides. This is not desirable because we are used to using the airing cupboard as storage for bed linen, towels etc. and a slimline cylinder of reasonable capacity, together with associated elements (expansion vessels etc.) would take up virtually all the space. The options appear to be: A heat battery (e.g. Sunamp Thermino) in the airing cupboard A modern cylinder located elsewhere, probably in the loft The thermino has advantages such as low heat loss, not requiring annual maintenance and not requiring Legionella cycles. The main disadvantages are initial cost and, if I understand correctly, the need to return to base for simple things like a faulty immersion. The modern cylinder has advantages such as lower initial cost, easier repair of faulty components. The disadvantages are higher heat loss (and being outside thermal envelope of house), requiring Temperature and Pressure Relief valve and associated pipework, annual maintenance. The particular point that is puzzling me at the moment is the effectiveness of a heat pump at actually bringing the hot water cylinder up to temperature and the optimum settings. For the sake of discussion I'd like to assume that the ASHP is a Vaillant Arotherm Plus 7kW (not yet decided, but it might simplify this discussion if we fix some items). When heating the hot water cylinder the higher the flow temperature from the ASHP the quicker the cylinder will reach temperature, but: The higher the flow temperature, the worse the CoP Lower flow temperatures imply lower transfer of heat energy into the cylinder If the heat energy transfer is lower than the ASHP can modulate down to then the ASHP will have to cycle on and off As I understand, cycling is bad for the ASHP components and is also associated wtih waste of electricity. The rate of heat energy transfer is connected to the flow temperature leaving the ASHP, the temperature of the cylinder water and the design of the coil. In terms of the coil, different manufacturers provide different information. For example, some provide coil surface area, some provide reheat time (in accordance with EN 12897, but I can't find the definition of this) and some provide a rating in kW (but I can't find the temperature difference that this is based on). Some (e.g. Thermino) I can't actually find any firm data at all. To summarise my main questions: Am I correct to think that the main aim would be to ensure minimum cycling of the heat pump? How low can a heat pump modulate down to at the sort of flow temperatures required for DHW and what is the associated CoP? Is there any firm data in the public domain on heat energy transfer into a Thermino? Apologies for the long introductory posting. If I'm still a member of the forum for long enough for subsequent posts then I'll try and keep them substantially shorter!