hot water provision using electricity only- UVC, TS, Sunamp... or just fill bath with a kettle?

[mattp22]

Hi Everyone, I've been reading the forum for a few weeks now- it's a great place for information and help, and very comforting so many people are going through the same level of head scratching i am currently experiencing! 

 

I am building a house on west coast of Scotland near Oban- SIP build with concrete block skin, then larch cladding, insulated foundation slab, 3G windows. Only have electricity on site, no gas. With SIPs I am hoping the house will have good insulation and air tightness values so heating requirements will be minimal. Bedrooms and bathrooms to have basic electric panel heaters/ towel rads as i'm not expecting needing to heat them much. Open plan living room and kitchen (approx 50 m/2) to have wet UFH. MVHR throughout. Wood burner in living room.

 

I am going in circles with how to supply sufficient hot water though.There will be 4 bedrooms, 4 bathrooms (2 shower baths, 2 just showers) and i am expecting to have a lot of visitors so potentially 8+ showers/ baths per day on a regular basis. One shower could be electric, but that leaves me with maybe 6 other showers/ baths to deal with on a daily basis when visitors come. High output drencher showers circa 15-20L/min (although i have no idea what my water pressure is yet- private supply coming off an 80,000 litre storage tank for whole village so i think it will be decent).

 

My initial plan (which i was originally pretty chuffed about devising myself ) was to use boiler wood burner and E7 immerser to heat hot water via thermal store (circa 1000 litres). Could also heat UFH too from bottom of TS, and I could install the TS myself. But seems I got ahead of myself- well insulated houses overheat with wood burners, TS have high heat loss apparently and the hot water provision tails off dramatically as water is used I've read. Now I feel like a scolded school kid! And the small matter of 1000L TS not fitting through the door too I suppose  

 

Sunamp- i read all the main 20+ forum pages and they appear problematic with electric only option. Plus are expensive. Plus seem like witchcraft. And I don't think they can do UFH. And the big one weighs the same as a highland coo.

 

So I am left with unvented cylinder heated directly via E7. But for 6+ daily showers/baths i would need something pretty huge, maybe even two UVCs, and professional installation. Not the end of the world space or purchase cost wise, but I am concerned about cost of heating water solely via E7 immerser (and potentially standard tariff if E7 hours don't suffice). I would also need to use a dedicated electric boiler just for UFH needs but hopefully I won't need it much.

 

So do I hook up some renewable sources to lower my electricity costs and increase SAP value? 4kw PV on roof to help during the day, E7 takes over at night. But my roof is a) east/west and b) in not so sunny Scotland. Maybe £4k cost if I can do most of install myself. Or ASHP to boost water temp to around 40 degrees then E7 increase to circa 60 degress at night. But cost for 5kw system ASHP seems to be £6-8k. 

 

Or is cost of renewable technology installation (and running costs for ASHP) greater than cost of just using mains electricity and swallowing high monthly bills?

 

So many questions.... my head is scrambled! Anyone else using electric only with/without renewables. Or do I go for cold showers only then guests won't overstay their welcome??

[ProDave]

Is this going to be a B&B?

 

The solution will not be one thing, but many.

 

The main issue with the sun amp is they can be heated by direct electric, or by a high temperature water say from a gas boiler, but not from lower temperature water from an ASHP. that's what made it a no for me.  Their main point is much lower standing heat losses so less or no overheating issue.

 

One immediate thought, is are some of your rooms only occasional use?  If so have two hot water systems, one for family (permanent residents) on all the time and one for the "guest wing" only on when guests are in residence.

 

Solar PV I managed to DIY install 4kWP for £1500 but that took some searching to get it that cheap.  £2000 is more realistic.  I seem to be self using about £250 worth of electricity from that each year.  An East / West split potentially suits maximum self use better than all south as you get an earlier start and a later finish to generation with less of a mid day peak.

 

Wood burning stoves CAN work in a near passive house standard build as long as you are careful.  I can burn our 4.5kW stove for 4 or 5 hours and give the whole house a useful temperature boost (and offset any other heating) without cooking ourselves.  I did some work on a straw bale house some years ago that had a WBS that put 10kW to water and only 2kW to the room and that heated a massive thermal store for hot water and under floor heating.  They only lit the stove every third of 4th day.

 

Several of us are using air source heat pumps to heat an unvented cylinder for hot water.  This might work if you could have a 2 cylinder system as above?

 

 

[mattp22]

On 19/08/2020 at 16:09, ProDave said:

Several of us are using air source heat pumps to heat an unvented cylinder for hot water.  This might work if you could have a 2 cylinder system as above?

 

Thanks @ProDave for comments. I had looked at Solar PV (albeit around the £4k mark) and ASHP but the payback time seemed very long compared to just using E7 tariff and accepting the larger electricity bills- like 10 or 15 years, however maths was never my strong point- I'd be delighted to hear otherwise.

I've spoken to OSO about their cylinders as I had read they have low heat loss, and they recommended multiple cylinders as you said- 3x300L which seems an awful lot, although budget wise still less than 1x Sunamp Uniq 12.

I'm still wondering about utilising the wood burner stove though and TS- if stove is not connected to hot water system then all that heat is lost. Seems sensible to try and capture some of the heat for hot water. I've found a external air boiler stove 2kw to room and 8kw to water. Does anyone else use a WBS to heat a bit of hot water? How much water could i expect (real life scenario) to heat if i had it lit for say 5 hours day? I found a calculator online which implied if i used all 8kw from the stove for 5 hours (heating water from 10 to 65 degrees C) then i would heat 625 litres! that would really help reduce the E7 bill!

 

 

[ProDave]

Think in simple terms.  An immersion heater is 3kW and for 7 hours at night on E7 that is therefore 21kWh maximum put into your tank.

 

An 8kW stove would put the same amount of heat into your tank  in a little under 3 hours.

[Thedreamer]

On 19/08/2020 at 15:24, mattp22 said:

 

Or is cost of renewable technology installation (and running costs for ASHP) greater than cost of just using mains electricity and swallowing high monthly bills?

 

So many questions.... my head is scrambled! Anyone else using electric only with/without renewables. Or do I go for cold showers only then guests won't overstay their welcome??

 

Yes, I'm running an exhaust air source heat pump to heat a 260 litre tank (our supplier also does a 300 litres, would a couple work for you?). I'm running it as a MEV system (which help to recover the steamy air from baths and showers) but you could draw the air from outside/garage if you have MVHR.

 

What I like about this system, is that it cost us £2,500 for the heat pump and cylinder (also has a back up dual immersion and acts as the fan for the MEV). Been running it for two months and the running costs is very cheap. My overall electricity usage is 10kwh a day for a family of four. The heat pump is fairly small compared to the larger ones often installed by other self builders but as it just does the hot water the output capacity is maximised through out the year. 

 

My general view is that a well insulated house need very little in terms of heating if I ever have a really cold period (I live in Skye, winters tend to be mild, windy and wet, similar to Oban I would imagine) I have our WBS and ours is not a token stove but well designed in the centre of the property, surrounded by dense concrete blocks. If we need a little bit of extra heating in morning then I'll use direct electric heating/heating from towel rails etc

[Nickfromwales]

Buy a dirt cheap DIY fit ASHP and fit a well insulated *500L UVC. Telford will spray extra insulation on for not much £££.

Yes, electricity is very simple and convenient, and if that's your choice then it will work. Simple and quick. Larger storage means you can load-shift off E10 instead of E7, *so you can top up midday too if needed.

 

Run the ASHP whenever you like, it's cheap enough to use not to worry about when, but anytime it's running on E10 you benefit even further .

 

Introducing wood burning into the heating / DHW system is a big leap from simplicity so be very careful about how you introduce that into your equations ( as the installation costs will be big ).

 

Difficult to say much more as you demonstrate a preference for options with a small capital expenditure. Log gasification attracts RHI, but you'd need room and at least 1000L of buffer tank, ideally more, plus a guaranteed / maintainable abundance of seasoned fuel stock.

[Nickfromwales]

90L here if you do go for the kettle option;

 

https://www.guinnessworldrecords.com/world-records/67159-largest-kettle

[mattp22]

3 hours ago, Nickfromwales said:

Difficult to say much more as you demonstrate a preference for options with a small capital expenditure.

 

lol, yes, i am a cheapskate, how could you tell  

i will start looking more into ASHP- they are less expensive than i thought actually- Daikin seem to get a decent name on here and a 5kw can be bought for about £2k without too much searching. I'd better start reading up how to fit them DIY though! Maybe see what deals can be found on good old Ebay too perhaps. One of the reasons i was against UVC was most manufacturers seem to be 300 litres max, but having a 500L option certainly puts a tick in the UVC column. Do you happen to know- if i wanted more DHW storage at a later date could I add on another cylinder without too much trouble?

 

Thanks

 

[Nickfromwales]

20 minutes ago, mattp22 said:

 

lol, yes, i am a cheapskate, how could you tell  

i will start looking more into ASHP- they are less expensive than i thought actually- Daikin seem to get a decent name on here and a 5kw can be bought for about £2k without too much searching. I'd better start reading up how to fit them DIY though! Maybe see what deals can be found on good old Ebay too perhaps. One of the reasons i was against UVC was most manufacturers seem to be 300 litres max, but having a 500L option certainly puts a tick in the UVC column. Do you happen to know- if i wanted more DHW storage at a later date could I add on another cylinder without too much trouble?

 

Thanks

 

lol..

 

Don't be daft and put a small UVC in now. It would cost a hell of a lot more to retrofit another cylinder, and to jump up a few sizes now is cheap enough. Be a cheapskate all you want, but don't be stupid  

Give Trevor @ cylinders2go a shout and mention the forum. He'll look after you. Lots on here have bought from him. 

[mattp22]

20 minutes ago, Nickfromwales said:

lol..

 

Don't be daft and put a small UVC in now. It would cost a hell of a lot more to retrofit another cylinder, and to jump up a few sizes now is cheap enough. Be a cheapskate all you want, but don't be stupid  

Give Trevor @ cylinders2go a shout and mention the forum. He'll look after you. Lots on here have bought from him. 

 

i would defo go for a 500 litre tank now, but i need to have enough water for potentially 8 showers a day, all with high flow rate, so i'm just not sure 500L will be sufficient. If i can daisy chain another UVC though then that would allow me to upgrade in future (and stop getting my knickers in a twist just now.) The guy i spoke to at OSO said i might need 3x300 litres UVC capacity, but i think until bathrooms are in and house being used i will not know for certain how much DHW is being used/ replenished quickly enough to cope.

 

I'll speak to Trevor- thanks 

 

[Nickfromwales]

16 minutes ago, mattp22 said:

 

i would defo go for a 500 litre tank now, but i need to have enough water for potentially 8 showers a day, all with high flow rate, so i'm just not sure 500L will be sufficient. If i can daisy chain another UVC though then that would allow me to upgrade in future (and stop getting my knickers in a twist just now.) The guy i spoke to at OSO said i might need 3x300 litres UVC capacity, but i think until bathrooms are in and house being used i will not know for certain how much DHW is being used/ replenished quickly enough to cope.

 

I'll speak to Trevor- thanks 

 

8 showers all at the same time / staggered / 4 in the morning and 4 in the evening??

INPUT!!!!!

[Alexphd1]

We have a mixed system consisting of 2x 500l stainless TS, 22kw log gasification, 8kw ashp, 8m2 solar thermal, 6kw PV. 

We haven't commissioned it yet. It's a very complicated and would be expensive install (my father and myself are ex heating engineers) and the material was sourced on the cheap ie ebay and buying the log boiler in eastern Europe (kotly.com).

Its designed to keep as much load of the heat pump as possible but the weak point is the TS needing a higher temp than a UVC. 

I would personally forget OSO and look at Telford tanks. 

Remember you can put a heat pump coil into a UVC and not use it and add the heat pump in later.

Edited August 23, 2020 by Alexphd1

[mattp22]

22 minutes ago, Nickfromwales said:

8 showers all at the same time / staggered / 4 in the morning and 4 in the evening??

 

There will be times when i have a full house of guests and we're leaving early in morning to go hill walking etc so i would anticipate at times 8 showers in the morning, all within a short time frame, plus more showers when we get back to the house in the afternoon. But other times there will just be 2 or 4 of us in the house. And to complicate things further, the house will be empty for some of the week/ a couple of weeks if we have to return to Glasgow for work etc. Several showers in quick succession was part of the reason i though wood stove + TS would work as the re-heat time would be very quick compared to E7 or E10 tariff, but that was before i started looking seriously at ASHP.

[mattp22]

14 minutes ago, Alexphd1 said:

We have a mixed system consisting of 2x 500l stainless TS, 22kw log gasification, 8kw ashp, 8m2 solar thermal, 6kw PV. 

We haven't commissioned it yet. It's a very complicated and would be expensive install (my father and myself are ex heating engineers) and the material was sourced on the cheap ie ebay and buying the log boiler in eastern Europe (kotly.com).

Its designed to keep as much load of the heat pump as possible but the weak point is the TS needing a higher temp than a UVC. 

I would personally forget OSO and look at Telford tanks. 

 

can i ask a question please (if you know the answer) comparing TS & UVC... if i am heating water on E7 tariff for instance- 7 hours at night on 3kw immerser- would i get the same volume of usable hot water from the 1000L TS as i would from a 500L UVC, or would extra volume of the TS 'dilute' the hot water in the TS and the overall water temperature in TS would be lower than UVC? My understanding is all hot water moves to the top of the TS or UVC but i've heard you get less usable water from a TS and I am wondering why. Thanks for tip on telford/ OSO too  

[Alexphd1]

I will be 100% honest and say I dont know exact answers, although I am a ex heating engineer it was more a case of stick in a gas/oil boiler bigger than needed and the jobs a good one back then.... there is better guys on here to answer that questions.

 

Only reason we went for a TS is it's near impossible (legally) to mix a UVC with a solid fuel system. 

A 500l UVC heated to 60 degrees will del 500l of water @ 60 degrees then a temp drop pretty quick when hot water is empty while a 500l TS heated to 60 degrees will (roughly) deliver water at low 50 degrees then start slowly dropping instantly until the tank is fully empty. But remember a shower is usually approx 37 degrees so you have a fair bit of HW before water no hot water left.

Edited August 23, 2020 by Alexphd1

[Alexphd1]

Remember if heating only by electric you can get tanks with 2 or 3 immersion ls ie 6 or 9kw so quicker to reheat the tank.

[PeterW]

Telford will fit what you want tbh - they will add additional Inmersions or extra tappings if you ask. A pair of 400 UVCs in tandem with a pair of top up immersions in the top 3rd would work. You could also get them to boost to say 75c just before E7 ends to give you additional “capacity” in the tanks. When there are only 2 of you there you would just run the one tank, pretty simple to time this as multiple channels on one timer. 
 

Flow wise you would run through T1 then T2, T2 being the hotter of the pair and the one that is your “always on” tank. You could W-Plan the ASHP to feed this one first and then only heat the second when a larger capacity is required. 
 

If there are only 2 of you, or DHW needs are low, then the one tank works fine and the other is essentially a buffer store. 

[Nickfromwales]

31 minutes ago, PeterW said:

Telford will fit what you want tbh - they will add additional Inmersions or extra tappings if you ask. A pair of 400 UVCs in tandem with a pair of top up immersions in the top 3rd would work. You could also get them to boost to say 75c just before E7 ends to give you additional “capacity” in the tanks. When there are only 2 of you there you would just run the one tank, pretty simple to time this as multiple channels on one timer. 
 

Flow wise you would run through T1 then T2, T2 being the hotter of the pair and the one that is your “always on” tank. You could W-Plan the ASHP to feed this one first and then only heat the second when a larger capacity is required. 
 

If there are only 2 of you, or DHW needs are low, then the one tank works fine and the other is essentially a buffer store. 

What about making T1 a thermal store? Take the UFH off it too so heating buffer plus DHW pre-heat via the DHW coil?

[Nickfromwales]

44 minutes ago, Alexphd1 said:

Remember if heating only by electric you can get tanks with 2 or 3 immersion ls ie 6 or 9kw so quicker to reheat the tank.

@jamiehamy has a 500L Telford with 4x 3kW immersions IIRC. 

[PeterW]

3 minutes ago, Nickfromwales said:

What about making T1 a thermal store? Take the UFH off it too so heating buffer plus DHW pre-heat via the DHW coil?

Could do although you would potentially want an ASHP coil in it if you’re going to want to heat it with different sources. Only benefit is that you could dump a wood stove into it but seems more hassle than it’s worth. 

[dpmiller]

I know a lot of folks here recommend Telford but I'll throw a nod in for World Heat- you're not forced to go through a merchant, fully bespoke as necessary and (essential for me) happy to deliver to NI.  Their coils seemed a bit bigger to me than some others I was looking at too.

[mattp22]

23 hours ago, PeterW said:

Flow wise you would run through T1 then T2, T2 being the hotter of the pair and the one that is your “always on” tank. You could W-Plan the ASHP to feed this one first and then only heat the second when a larger capacity is required. 

 

yes that is what i thought too, so i would always have 500L main cylinder with potential 500L backup when required. A UVC manufacturer sent me this diagram today though for parallel connection- i read from this i would need all 3 cylinders to be heated at same time to same temperature to balance my hot water feed? If one cylinder is cold the cold will feed into the main DHW pipe and lower the temperature of everything?

 

 

[PeterW]

You want series fed not parallel. Parallel fed can give you bigger volumes but it means everything is heated to the same temperature and tbh you may as well just have one massive cylinder. 
 

Pipe the DHW in 28mm from main to manifold and you won’t have a problem. 

[PeterW]

1 hour ago, mattp22 said:

 

yes that is what i thought too, so i would always have 500L main cylinder with potential 500L backup when required. A UVC manufacturer sent me this diagram today though for parallel connection- i read from this i would need all 3 cylinders to be heated at same time to same temperature to balance my hot water feed? If one cylinder is cold the cold will feed into the main DHW pipe and lower the temperature of everything?

 

 

Actually looking at that they list a “multi function valve” on the the top of the UVC. Wonder if they lock out the cold tanks ..?

 

Seems a lot to go wrong - series UVC would work fine and no valves or moving parts required. 

[SteamyTea]

On 23/08/2020 at 19:24, mattp22 said:

enough water for potentially 8 showers a day, all with high flow rate

Have you actually checked the flow rate to your house and what you can realistically supply to 4 showers running at the same time?

 

You can reduce the flow rate, 9 litres/minutes is a pretty good shower.

 

Avoid a wood burner, they are horrible, and not as cheap as people think.