Using water as a dynamic heat sink/source  - Page 1
Forum section: electronics / general

author: max_torque
author_rank: Super Contributor
timestamp: April 12, 2020, 03:54:45 pm
content: Has anyone considered using a volume of water (well water/gylcol mix) as a dynamic heat sink for a system using a heat pump?A 1000 litre IBC is cheap, could be buried in a pit, insulated with some normal insulation, and with a heat pump arranged to be able to heat or cool that volume, would be a significant energy store, enabling dynamic load shedding espically wrt to cheap grid energy / solar power?1000 litres of 70/30 water glycol is 1057 kg, has a specific heat of 3.74 kJ/kg.K, and with a heat pump using a refrigerant to coolant exhangers to avoid icing (no ambient air containing moisture to freeze up) and probably avoiding boiling too (makes system simpler as it won't have to be a pressure vessel) could probably operate with a 90 degC deltaT if necessary on that coolant store. That means around 100kWh of energy can be dynamically exchanged.I live the UK, where we tend to have cold nights, and warmer days, and our solar load is very peaky, and our grid electricity costs are highly industry demand driven, and recently have been going negative overnight!So, in the winter, when i say want to heat my house for 6 hours in the evening (4pm to 10pm) i can use a cheap solar hot water array on the roof to heat the coolant store, and if that is insufficient (which it will be for most of the winter) then i can turn on electric immersion heating during cheap rate electricity the night before.In summer, if i want to cool my house (increasingly required as our summers get hotter) then i can simply reject heat from the house into the coolant store, and over night, when it's cooler, use a simple cheap air/water radiator to reject that heat to ambient air, over a longer period.This, at first glance seems a sensible system, and relatively cheap, using a heat pump to move heat around, and cheap components that could certainly be sourced (sic) second hand in order to build it?By leveraging a heat pump, the energy i ultimately pull from the grid can be around 3 times lower than the heating/ cooling power, and of course, it would be possible to move that to a solar electricity based system eventually....Have i missed something important here? I'd have to run a simulation over a typical UK year to see how it stacks up i guess

author: Marco
author_rank: Super Contributor
timestamp: April 12, 2020, 04:30:54 pm
content: Don't see how solar collectors are ever worth it any more, just put down more PV.Any heatpump system will have a thermal buffer to prevent cycling ... just making that huge with insulated IBCs is certainly an option. Given that you don't have net metering it might often make sense to run the heatpump and buffer heat/cold rather than feed in.The only problem I foresee is how to automate it, given that Smart Export Guarantee requires a certified system ... will there be certified systems to dynamically optimize between thermal storage and feeding in?

author: MarkF
author_rank: Super Contributor
timestamp: April 12, 2020, 04:32:43 pm
content: Ever hear of Geothermal Heat Pumps?

author: Marco
author_rank: Super Contributor
timestamp: April 12, 2020, 04:52:59 pm
content: Quote from: MarkF on April 12, 2020, 04:32:43 pmAquifer availability isn't exactly universal. Using insulated pools just under the surface instead is quite common.

author: coppice
author_rank: Super Contributor
timestamp: April 12, 2020, 04:55:24 pm
content: Quote from: Marco on April 12, 2020, 04:52:59 pmWhat is the relevance of aquifers?

author: Marco
author_rank: Super Contributor
timestamp: April 12, 2020, 05:01:12 pm
content: Quote from: coppice on April 12, 2020, 04:55:24 pmNeeds less boreholes. If you need a ****ton of boreholes to store heat directly in small regions near the boreholes I'm not sure it still makes sense to store thermal energy underground, otherwise why do they do the insulated pool systems?

author: coppice
author_rank: Super Contributor
timestamp: April 12, 2020, 05:07:23 pm
content: Quote from: Marco on April 12, 2020, 05:01:12 pmMost people don't do use insulated pool systems. Most people do what is in the image a few messages back. They put a network of tubes 1m to 2m below the garden. Soil insulation is sufficient that 1m down the temperature hardly changes between summer and winter. So, you can fairly efficiently push heat into that soil as you cool the house in the summer, and then draw it back when you need to warm the house in winter.

author: jc101
author_rank: Frequent Contributor
timestamp: April 12, 2020, 05:10:54 pm
content: A long time ago now I worked for years in the Sinclair Research building (Ex Clive Sinclair, Spectrum computers etc.). For it's time it had an advanced heating / cooling system.In the basement was a huge water tank, overnight that would be heated by a heat pump that took water from a bore hole (it used to be a mineral water bottling plant back in the day) to store in the tank. That heat was then used to heat the building. The bore hole water was a steady 12c all year round, and when it worked it was great. In the summer, the bore hole water could be pumped up to an exchanger on the roof to cool the air in the building.Sadly, many years of building alterations and no-one understanding how it all worked meant it was eventually removed. The basement was turned into offices, and I believe is now a room full of UPS gear.We used to get letters from all over the world asking for help with old Sinclair computer gear, if we could help we did reply.Needles to say, we had a banister around the stairs when I was there....

author: Marco
author_rank: Super Contributor
timestamp: April 12, 2020, 05:39:28 pm
content: Quote from: coppice on April 12, 2020, 05:07:23 pmCan you show any such system which actually charges the soil to a proper high temperature (lets say 20 degrees above the natural soil temperature at that depth) and show it retaining that heat for significant time when there is no load?AFAICS storage in these systems is mostly just a legacy use for surplus heat from solar collectors, for which even an extremely lossy storage is better than nothing. With PV getting ever cheaper and storage competing with feed-in, the storage needs to be somewhat low loss.

author: coppice
author_rank: Super Contributor
timestamp: April 12, 2020, 05:41:53 pm
content: Quote from: Marco on April 12, 2020, 05:39:28 pmIt was good enough for rich people to have summer ice cream in medieval times.

author: Marco
author_rank: Super Contributor
timestamp: April 12, 2020, 05:49:42 pm
content: Quote from: coppice on April 12, 2020, 05:41:53 pmYet they were doing it wrong ... wood, straw and air were much better insulators than soil.

author: max_torque
author_rank: Super Contributor
timestamp: April 12, 2020, 05:57:21 pm
content: Quote from: MarkF on April 12, 2020, 04:32:43 pmof course.But what i am suggesting is subtly different! I am not using the water as an energy source or sink, i am using the water as a buffer, so that water, unlike a GSHP, needs to be well insulated from its surroundings!GSHP pushes heat into, or pulls heat from the earth and rock. My system will take heat from other sources, and simply use the water as a very mobile, very high specific heat "battery" in effect. The idea relies on the fact that we don't have the heating constantly, tend to want more heat at certain times a day, and that thanks to industries running mostly during the day, we have a net energy surplus overnight, meaning energy costs can invert (ie they PAY YOU to use electricity!)I could cheaply put in say 20 kW of mains electrical immersion heaters, and charge my liquid heat battery,makingmoney as i do so, and then slowly deplete that energy as an when i need it to heat my house, or warm water etc

author: max_torque
author_rank: Super Contributor
timestamp: April 12, 2020, 06:00:52 pm
content: Quote from: Marco on April 12, 2020, 05:39:28 pmWhich of course drives one towards a larger reservor, because the surface area to volume ratio improves continuously as the size of that reserve increases!

author: duak
author_rank: Super Contributor
timestamp: April 12, 2020, 07:22:20 pm
content: 1000 kg of water is a cube only one meter on a side. Not an unmanageable amount. I expect insulating it will be interesting.I looked into doing something like this in 2007 when energy prices were high. There were at least two German companies providing parts for systems like this: Stiebel-Eltron and Viessmann. I also remember that Glauber salts were also used to store heat because it changes phase around 30 deg C.In the end, I went with a high efficiency water heater, furnace and heat pump. The climate here in Vancouver, Canada is similar to that of the UK. On the other hand, we have cheaper electricity and natural gas. If energy prices were higher or if there were shortages, it would change the calculus to adding solar collection and storage. BTW, we had a major failure in one of the natural gas pipelines recently. People were asked to reduce gas useage. I was able to run the entire air and water heating system on electricity with a few simple changes.About the Sinclair building. One of my employers started as a small company in a building very much like Sinclair's. It used a pond as a heat store and had water pumps in the basement and heat exchangers for the HVAC system on the 5th floor. As far as I know, it used common parts and controls and was reasonably reliable. Like anything that mixes water, metal and electricity there's trouble sooner or later. eg., autos, washing machines, etc. It would be interesting to see how effective and efficient it was vsi-a-vis a standard HVAC system.The building was designed and built in the early 80s for the provincial government to act as an incubator for entrepreneurs. The company expanded and ended up taking over the entire building. It turned out the design wasn't right for entrepreneurs because they usually wanted their own entrances. The building also got a bad reputation because a number of the tenants were considered to be running scams. It became a location for filming various TV series because it looked futuristic.

author: jc101
author_rank: Frequent Contributor
timestamp: April 12, 2020, 07:33:45 pm
content: The Sinclair building was very efficient for it's day. The problem was internal walls were thrown up which caused airflow / circulation problems. That started the downward spiral as successive teams tried to fix it without really understanding how it was originally designed, and people moving the walls about. After all, it was a home grown design by Clive himself.The McLaren Technology Centre (https://en.wikipedia.org/wiki/McLaren_Technology_Centre) uses the artificial lake to cool the building and the wind tunnel. It's a really impressive building to visit and have a poke about. The F1 cars are built in what looks like a sterile workshop, everything is pure white, if *anything* dripped or fell of it would stand out a mile.Rather Tham 1m3 of water, their lake is 50,000m3, but is only used for cooling.

author: max_torque
author_rank: Super Contributor
timestamp: April 12, 2020, 07:44:27 pm
content: Quote from: duak on April 12, 2020, 07:22:20 pmIm thinking a block work "bund" lined with 100mm of foil faced PIR insulation, surrounding a 1000 litre IBC.U values of around 0.022 W/mK , roughly 6m^2, say average 50 degC delta to ambeint, so that's a pretty low heat loss. Of course, air drafts and the necessary pipe peircings will reduce that insulation performance significantly, but at a first look it doesn't look too hard to do.

author: Marco
author_rank: Super Contributor
timestamp: April 13, 2020, 05:31:30 pm
content: Quote from: max_torque on April 12, 2020, 05:57:21 pmI'm not sure that makes sense. For legionella reasons you want your hot water circuit for tap/showers to be much hotter than temperatures which can still provide all the heat for your central heating (with low temperature radiators or floor heating).

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 14, 2020, 12:36:40 am
content: What does really well for thermal storage is air conditioning using ice, since then you can take advantage of the phase change effect and end up with similar energy density to using batteries, at a much lower cost.Quote from: Marco on April 13, 2020, 05:31:30 pmLargely a non concern with chlorinated city water (actually, it's becoming more common to use chloramine which is more effective than just chlorine), but even if it is, it can be solved pretty easily with a heat exchanger so the tank water is separate from potable water. Most likely some sort of heat exchanger will be the most economical choice anyways so the tank doesn't have to handle the full pressure.

author: max_torque
author_rank: Super Contributor
timestamp: April 14, 2020, 08:19:42 pm
content: The important point is that the bulk store is1) An energy store, not a temperature storeand2) Is never used for end users, so can contain corrsiion and biological inhibitors as necessaryThe key tech is the heat pump that sits between the various bits of the system and "converts" between the different temperatures of those systems.For example, i can use a roof mounted solar water heater, to lift the bulk heat store by say 20 degrees. That's too little to use directly as hot water for the end user, (heating or washing) but the heat pump can leverage the heat in the heat store and convert it to a more useful temperature in another part of the system.

author: Marco
author_rank: Super Contributor
timestamp: April 14, 2020, 08:45:17 pm
content: I think heatpumps will just circulate water from the buffer tank through central heating directly if it's hotter than their max return temperature. If so you only really need a heat exchanger to heat up the "cold" water input for a boiler, the IBC would be the heatpump buffer. Although to be able to switch over between heating and cooling temporarily without dumping all the storage energy it might be better to have a separate smaller buffer so you can decouple the IBC for a bit.I just don't see how solar collectors make sense any more, any room they take would be better occupied by PV.

author: wraper
author_rank: Unknown
timestamp: April 14, 2020, 08:46:21 pm
content: Quote from: Marco on April 12, 2020, 05:39:28 pmWhy would you want to "charge" the soil? What you want to avoid is that soil temperature changes significantly (heat pump efficiency drops) and increase heat exchanger area if that happens. Earth is not storage, it's a heatsink with stable temperature and basically infinite thermal capacity.

author: Marco
author_rank: Super Contributor
timestamp: April 14, 2020, 08:48:41 pm
content: Quote from: wraper on April 14, 2020, 08:46:21 pmBecause a heat pump still takes power ... a charged thermal storage allows you to do heating/cooling with only the pump consuming power.

author: wraper
author_rank: Unknown
timestamp: April 14, 2020, 09:02:48 pm
content: Quote from: Marco on April 14, 2020, 08:48:41 pmYou don't understand the core idea about using heat pump. You don't use it to store energy somewhere (soil). If soil temperature changes, it's unwelcome side effect. Air heat pump works the same, just less efficient as heat pump needs to deal with much larger temperature difference.

author: Marco
author_rank: Super Contributor
timestamp: April 14, 2020, 09:14:53 pm
content: Quote from: wraper on April 14, 2020, 09:02:48 pmMost heat pumps have small storage buffers to prevent frequent cycling ... so energy storage is a standard feature. OP wants to have a little more storage so he can turn on the heat pump (or even an electric heater) when electricity is cheap and it can carry heat across a couple days.Under ground storage systems are being used too (ATES/BTES). But it's expensive and I doubt the storage efficiency is very good compared to having massive insulated water tanks.

author: max_torque
author_rank: Super Contributor
timestamp: April 15, 2020, 10:25:24 am
content: A "heat pump" is basically the same in the thermal environment as a DC/DC converter using an inductor is in the electrical environment. The inductance in a DC/DC allows one to move current against the normal direction of potential, the phase change of the working fluid in the heat pump system allows one to move heat against the normal temperature gradient.How you use either is not fixed.In my case, a heat pump would allow me to collect a large amount of "Low level" heat energy, energy at too low a temperature to be useful, and then once i have cheaply stored that energy, to at a later time access it, and "concentrate it".This means i can use very cheap heat sources,like solar water heater (which can be as cheap as a length of hose black hose pipe coiled on the flat roof of my workshop) to charge my heat store. It also allows me to potentially pull my bulk store BELOW ambient temperature, and so be able to access a greater total amount of energy from that store (like being able to discharge a capacitor to a negatoive voltage).But, the critical point, is that the system effectiveness, in terms of $ per kWh of heat, is driven by non physical metrics, broadly the fact that our electricity cost is not fixed, but varies by time of day, so by being able to regulate when i take power from the grid, means i can also leverage those differences in cost to add value to my system. A simple AC electrical immersion heater can again be very simply and cheaply added, whcih can be used to "charge" the store during times of cheap electricity, perhaps even when the price is actually negative!

author: fcb
author_rank: Super Contributor
timestamp: April 15, 2020, 01:57:42 pm
content: What about two IBC's. One heavily insulated (hot water store) and one exposed to the subsoil.If you can get the solar collector to work without a pump (?) then you have a tank of warm/hot water for night/winter use and a cold tank for driving some sort of aircon in the summer.Just how hot do typical solar collectors get?

author: Marco
author_rank: Super Contributor
timestamp: April 15, 2020, 08:37:28 pm
content: The vacuum ones can heat it to boiling, the problem is they are expensive ... and an immersion heater running from PV power can get pretty hot as well, it can even do it on diffuse light.Without an extensive pipe network below the frostline or boreholes it's unrealistic to expect to be able to dump/extract significant heat to/from the soil. Just the contact surface of the IBC is going to be way yoo slow.PS. I wonder if a lot of houses in a dense urban area start using ground source heatpumps if the frostline will drop significantly.

author: Someone
author_rank: Super Contributor
timestamp: April 16, 2020, 12:00:12 am
content: Quote from: max_torque on April 15, 2020, 10:25:24 amAlso consider that the thermal mass could be more effective if inside the houses insulation shell. Cost effective solutions can even be found around "resizing" (to apparently ridiculous extents) normal components of the heating and cooling systems.

author: Someone
author_rank: Super Contributor
timestamp: April 16, 2020, 12:03:19 am
content: Quote from: Marco on April 15, 2020, 08:37:28 pmThere are some good works on that topic, an easy one for example:https://www.withouthotair.com/c21/page_152.shtml

author: ogden
author_rank: Super Contributor
timestamp: April 16, 2020, 01:09:47 am
content: Quote from: wraper on April 14, 2020, 09:02:48 pmRight. Geothermal heat pump (GHP) do not store energy. Then there is ground source heat pump (GSHP) which does exactly that -freezecool-down (big enough) land mass during winter in hope that it will be heated during summer. I would avoid installing GSHP because you may end-up with permafrost under your harden and little to no heat during winter.

author: max_torque
author_rank: Super Contributor
timestamp: April 17, 2020, 11:20:35 am
content: There's actually another interesting possibility that using a Heat pump as a T/T converter (Temperature to Temperature) opens up, and that is to run the solar hot water collection loop at a mean temperature BELOW ambient! The problem with solar hot water panels is that because they conventionally need to be above ambient, they must be well insulated to avoid most of the thermal radiation energy from simply "leaking" out into the surrounding colder environment.Realistically, you want an outlet water temp of lets say 60 degC, which is hotter by at least 30 degrees than most ambient environments.But with a heat pump, you can cool the entry temperature of the water going into the solar panels to below ambient, far below, and now, not only do you collect practically 100% of the solar radiation (only reflection now counts as a loss) but you also actually gain heat from the environment!This means cheap panels, and very high efficiency, and the ability to collect heat even on a cloudy day, where conventional solar hot water panels cannot, because there heat loss exceeds the incoming radative gain.

author: Marco
author_rank: Super Contributor
timestamp: April 17, 2020, 02:43:56 pm
content: It doesn't get you anything, there is never any reason to pump something below ambient in heating. Yes, you're also heating something up with that pumping .... but you could just pump against ambient instead and be more efficient. While the solar collector could take water at ambient and get more useful energy relative to ambient, which you have at infinite capacity.Air ambient is always there, nothing below it makes sense. A heat pump is not a heat engine, being able to get larger temperature differences between fluids might be potential energy, but it's not energy you can use.

author: ogden
author_rank: Super Contributor
timestamp: April 17, 2020, 04:38:34 pm
content: Quote from: Marco on April 17, 2020, 02:43:56 pmReally? How do you think air source heat pumps are able to operate then?

author: Marco
author_rank: Super Contributor
timestamp: April 17, 2020, 05:11:07 pm
content: Heatpumps are non intuitiveI guess you could just use a water to water heatpump and use the output of the primary side of the heatpump as the input of the solar collector, and connect the output of the solar collector as the input of the primary side of the heatpump ... if the collector can't raise the temperature above ambient though it will not get you anything.It would be more effective to heat the primary side water to ambient with a simple fin radiator, and only then heat the refrigerant up from ambient with the collector.

author: ogden
author_rank: Super Contributor
timestamp: April 17, 2020, 06:21:11 pm
content: Quote from: Marco on April 17, 2020, 05:11:07 pmGood point. AFAIK most solar hot water collectors are used without heat pumps, they usually are just (pre)heaters for boilers. When it is about heating then again - during time/season when you can extract actual heat from solar collector, most likely you don't need any heating at all. You rather need cooling. In result solar-assisted heat pump installations are not that popular and usually of industrial scale.

author: max_torque
author_rank: Super Contributor
timestamp: April 17, 2020, 08:32:05 pm
content: Quote from: Marco on April 17, 2020, 02:43:56 pmOh dear, i hope you don't need to use physics for your day job...The beauty of storing heat energy at a constant temperature is that you can manage the losses, because those loses are driven by the thermal graident to the ambient environment.For example, i have two cups of water on my desk, in a room at 25 degC. The water in one cup is at 50 degC, the other is at 25 degC.. Which cup looses more energy to it's environment ?Solar hot water heating panels normally have to tread a fine line, they have to allow as much solar radiation into the coolant medium, but let as little heat energy escape. Up on your roof it's probably cold, and windy, if the solar radiation heats the water in the panel to say 50degC, then that's significantly higher than the environment, so no matter how good the insulation is, some of the heat energy gathered from the radiation is lost.Now consider a panel where the water temperature in the panel is not allowed to get above ambient. What are the loses now? Can you see the advantage?Of course, the trade off becomes a balance of the CoP of your thermal converter (heat pump) vs the delta T of the system. The higher the deltaT, the lower the CoP (RE: carnot cycle efficiency).This is what i shall run some simulation to characterise, as there is plenty of data on practicalable heat pump CoP vs deltaT with different refrigerants.The single benefit of a water storage system is however cost, or lack of it. Using a thermal temperature converter allows you to utilise low level heat, and that means cheap storage. My 1000 litre ICB, with a working temperature range of +- 25degC from ambient contains the same amount of energy as a big Tesla Battery (~100kWh) and yet the plastic tank costs around $100 and the water in it is effectively free! It also can be charged and discharged an infinite amount of times, and the charging rate, thanks to the higher specific heat capacity of water is actually pretty good too

author: Marco
author_rank: Super Contributor
timestamp: April 17, 2020, 11:59:56 pm
content: Quote from: max_torque on April 17, 2020, 08:32:05 pmHeat is energy, but it's not necessarily useful energy.QuoteThe one which has something to lose.QuoteLets say for a moment the collector heats it up to exactly ambient temperature, what according to you would be optimal ... what did that get you? You don't need to use a solar collector for what a radiator can do, in fact you shouldn't because a solar collector is designed to be a terrible radiator. When there is no sunshine the radiator will still heat it up to ambient, but a good solar collector will do nothing. The radiator always works, the collector doesn't.The collector is for heating above ambient.

author: richard.cs
author_rank: Super Contributor
timestamp: April 18, 2020, 12:30:28 pm
content: Or to put it another way, you already have an infinite heat source/sink at ambient temperature, which is cheap to couple into with a conventional refrigerant:air heat exchanger. Taking heat from a solar collector at ambient temperature has no advantages* over taking the same amount of heat from the ambient air. If you run the solar collector below ambient then you'll be pumping heat against a bigger temperature differential and your COP will fall and you'll have to put more energy in to move that heat than if you took it from ambient.It's a valid point that using a solar collector to feed a heat pump allows you to benefit from a collector too cool to usefully heat water, but this is only true if your solar collector is still above ambient so that it improves your COP compared to pumping form ambient. e.g. in a 10'C ambient, pumping heat from a 40'C collector to heat domestic water to 60'C is a good idea, but only because it improves your achievable COP (the theoretical max goes from 7 to 17 but you won't get near that in practice, looking at some graphs online you might go from 4 to 12 which is still a big benefit).*well, one maybe, it won't ice up.

author: max_torque
author_rank: Super Contributor
timestamp: April 18, 2020, 05:47:14 pm
content: As you rightly spotted, the ability to avoid freezing is significant, but the other advantages are:1) increase the operating temperature range of my coolant store. This basically gets you a "bigger" storage system because you can swing its temperature a greater amount.2) It enables a much cheaper heat source. To pull say 5kW continuously from the air, and avoid freezing in the UK especially is difficult. Air has a low specific heat capacity, and contains a lot of moisture. Using 1 tonne of water as a dynamic store and a cheap solar array (operating close to ambient it can be very cheap indeed, think coiled up, black painted rubber hose pipe! In winter, where air temps are typical around 6 t0 8 degC, that becomes particularly problematic.3) for a lot of a typical year in the UK, if i want my house at say 18degC, then i'm going to need to be heating it in the evening and overnight, and cooling it during the day, that can be done without any external heat source using a big enough storage tank, by just pushing low level heat backwards and forwards.You point about the balance between thermal gradient and CoP is very valid, as i previously mentioned, hence the plan to do some simulation with realistic heat pump numbers to see if a "sweet spot" exists, and what sort of control algorythm would be needed to optimise the system for the lowest energy inputAs i said originally, the primary aim to to be able to use "cheap rate" electricity (or 'lecy from a local solar PV array, that may have an erratic output) to replace my current energy supplied by my gas boiler. To do that with a purely electric system is very expensive, because batteries are expensive, but water tanks and water are not.......

author: Marco
author_rank: Super Contributor
timestamp: April 21, 2020, 12:20:13 am
content: Quote from: max_torque on April 18, 2020, 05:47:14 pmAn unreliable heat-source.QuoteThe ice has a lot higher moisture density, which is to say it's far faster to melt than to accumulate.QuoteNah, an IBC is days worth of storage ... you don't want to be pushing it this way and that all the time, any time you miss the mark (all the time) you waste a ton of energy. I think a large tank for heating and a smaller tank for cooling makes more sense, most of the time when you're cooling you'll have PV electricity after all.If I were going to do it, I'd get something like a Panasonic air-to-water TCAP monoblock. Connect the IBC and a smaller tank as buffers. Throw immersion heaters into the IBC. Have an electric boiler for hot shower/tap water and route inlet water through a heat exchanger in the IBC (saves you significant on the amount of electricity used by the boiler). Or just use an existing gas boiler if you have it, but still with the heat exchanger.I think for the most part you could let the standard controller just do its own thing. Just need to add some extra control to switch the buffer tank when you switch to cooling and turn the immersion heaters on when you want to use excess power. Maybe the heatpump will need some additional duty cycle limiting though with such a huge buffer, going to take a while to get up to temperature.Of course you're only going to save money if you count your time as free

author: tszaboo
author_rank: Super Contributor
timestamp: April 21, 2020, 11:00:33 am
content: Quote from: max_torque on April 12, 2020, 07:44:27 pmYou need almost a cubic meter if isolation for that, and that isolation has almost zero weight. Ground water can actually push objects, like empty tanks out of the ground, and this could easily happen to this. Or you dont make it waterproof, and then it will be soaked in water, and U value is off.