DHW systems - thoughts?

[Gill]

 

I have another thread relating to heating that I'd gone a bit off topic into DHW so thought I'd start something in the right spot to request advise and opinion. 

 

Current setup : immersion.

Probably 20 plus years old.

Not easily accessible to insulate further.

Very little control - we added a timer to reduce energy use 

Wired to economy 7 only so no mechanism to top up outside eco 7 hours. 

Mains Flow rate - 1 ltr every 2.5 seconds 

Pressure - not known at the moment 

Useage ltr - max 300-400 per day. Average 200

 

Wish list 

Reduce /remove attic headers to make the attic space one day habitable 

Easy control / adjustment of when the water is heated and to what temp on any day 

Ability to top up outside of eco 7 hours 

Pv ready. One day we'll get this in and I don't want to rework what we put in now 

Energy storage (as hot water). No battery as its not yet financially viable. Any spare pv we'd want to use to heat water and store. 

Faster delivery of hot water than the current 2 mins lead time 

Low maintenance system 

 

Constraints 

No mains gas 

Plan to heat house with A2a and avoid any wet system install. Basically ASHP discounted. 

 

Systems considered

ESHP - not convinced on this taking heat from the house but could have potential gains even if draw /exhaust from outside. Header tanks not required. Fast delivery of hot water. Not cheap. Potential maintenance. Could be very cost efficient running over eco 7 hours only (if possible) . 

 

New immersion - doesn't remove the header tanks. Cheap. Reliable. Not sure how this integrates with pv. Slow delivery of hot water. 

 

UVC - removes need for header tanks if I'm understanding correctly. Not sure how this integrates with pv. Gives faster delivery of hot water? Price ranges vary but cheaper than eshp. 

 

Suffering from paralysis by analysis and lack of expertise to make any real sense of any analysis I do! On the plus side, I'm not alone as two of the companies I've spoken to about DHW systems were astoundingly less knowledgeable than me. 

 

That does leave me seeking out the collective build hub hive mind for advice. 

 

I think to benifit from a future pv install I might need to combine systems so there is ability to have hot water on demand but also ability to store hot water (feed to the main water heating system?).

 

Is that total nonsense and I've missed a simple solution? 

 

Any input appreciated. 

 

 

 

 

 

 

 

[gregh]

Am also looking for solution to electric DHW. Think I've landed on 300L UVC with dual immersion. Use a timer for overnight heating on cheaper rates. When PV is added, use an eddi to divert excess to immersion where possible.

[Gill]

2 minutes ago, gregh said:

Am also looking for solution to electric DHW. Think I've landed on 300L UVC with dual immersion. Use a timer for overnight heating on cheaper rates. When PV is added, use an eddi to divert excess to immersion where possible.

 

Thanks. That's interesting. No header tank required with this setup? 

Edited April 5, 2023 by Gill

[gregh]

Just now, Gill said:

 

Thanks. That's unteresting. No header tank required with this setup? 

 

Not with UVC, no. We also want to lose the tank in our loft.

 

Am also going to try to find an UVC with a couple PT1000 temp sensors if I can (might be a custom job). Can hook them up to the eddi and make it a little "smarter", if I understand things correctly.

[Gill]

3 minutes ago, gregh said:

 

Not with UVC, no. We also want to lose the tank in our loft.

 

Am also going to try to find an UVC with a couple PT1000 temp sensors if I can (might be a custom job). Can hook them up to the eddi and make it a little "smarter", if I understand things correctly.

Sounds like a simple one solution stop.

 

I do wonder though on a sunny day (they happen more frequently in Glasgow than advertised), we'd probably have the ability to heat more water. We need to assume daily forecast of grey and miserable and would therefore be heating the tank to required temp on overnight eco 7 rate. This is where my thinking on some 2ndary tank comes from. 

 

Temp sensors and some automation might help here. Standard tank temp of 50 (or whatever is a healthy hot water store temp) unless the pv is kicking in, in which case ramp the water temp up. Some type of temp regulator on outlets involved which may or may not exist as standard. 

[Marvin]

10 hours ago, Gill said:

Useage ltr - max 300-400 per day. Average 200

A few thoughts

How many people in the building?

How many bedrooms?

Do you have a south facing pitched roof that is not shaded?

You have about 1200 hours of sun a year.

 

We have PV, a hot water cylinder and an excess power diverter. And it works very well.

 

 

 

[JohnMo]

Most UK manufacturers seem to do custom cylinders if you want them.  So you could in effect have any number of immersion heaters at different levels.  So you could for instance, have E7 one dedicated, have one at a high level for not so sunny days, this would then move to the a lower one once the top is satisfied on a really sunny day.

 

@Nickfromwales go to place seems to be Trevor at cylinders2go.  So it may be worth having a discussion direct with them, other suppliers are available.

[SteamyTea]

This is what I have/started with.

 

200 lt, bog standard, vented, E7 cylinder. Heating elements in the base and the top.  All very standard and cheap.  Had to replace cylinder after about 28 years.  Small heater tank in loft.

I have fitted a twin impellor shower pump to the shower/bath.  This was mainly to make a decent shower, between 9 and 11 lt/minute flow rate. Pressure is irrelevant as it is flow rate.

I added extra insulation inside the cupboard it sits in.  This is a combination of PIR sheets and mineral wool.  Works very well, reduced the standing losses by over 1 kWh/day (standing losses are a problem on E7 as some people want to bath in the evening, I don't apart from a quick shower).

Initially I set the lower E7 thermostat to 65°C, but have reduced it to 50°C now.

I then fitted a timer to limit the E7 heating window (nominally midnight to 7 AM) to 4 AM to 7 AM).  This gives it plenty of time to heat the cylinder, settle and a reheat, before I use any (which I try to do after 7 AM so no extra reheating).

This worked well and almost halved the energy usage, some of that will have been because I fitted a shower and use less water).

Last year, about May I think, I decided to experiment with the top immersion heater, the thinking being is that I do not use all the 200 lt of stored water.  So I fitted another timer that switched the top element on between 5 AM and off at 7 AM.  I also set the temperature higher to 65°C.

This worked very well in cutting energy usage, but did, on a couple of occasions, mean I had a luke warm shower after work (not so bad in the summer months, horrible when the house is a but cooler).

Because I swapped my morning bath (my little luxury and seems to help my aches and pains) to a shower, that probably helped in reducing water usage, and there for energy usage (we were asked, by SW water (one of the countries largest polluters) to cut usage by 5 lt/day in return for £30 off our bill, achieved the target).  This year, I may try and gauge if the saving is water usage or less standing losses.

I may also try heating the water with the lower element for a day, then heating the top for a day, and then back to the lower element.  The mean usage should be the same, but because of the need to have DHW at least 35°C, there may be less risk of having a cold shower.

 

I am in a lucky position because I live alone, this mean that if there is not enough hot water, I am only shouting at myself.

Energy reducing should not be down to just one person in the house making changes, it has to be everyone, then there is plenty to go around.

The biggest changes will be reducing water usage, will over shadow everything else.

 

Aunty Beed has an interesting program on about water.

https://www.bbc.co.uk/sounds/play/m001k0dq

 

 

[Gill]

3 hours ago, Marvin said:

A few thoughts

How many people in the building?

How many bedrooms?

Do you have a south facing pitched roof that is not shaded?

You have about 1200 hours of sun a year.

 

We have PV, a hot water cylinder and an excess power diverter. And it works very well.

 

 

 

 Two people in the building. Occasional overnight visitors. 

2 bedrooms. 

Good size unobstructed South facing pitched roof. I estimate 5x3 would be suitable for panels. 

Google tells me 1216 sun hours in Glasgow. 

[SteamyTea]

14 hours ago, Gill said:

ESHP - not convinced on this taking heat from the house but could have potential gains even if draw /exhaust from outside

I don't think it would, at worse, be worse than resistance heating.

Houses need to expel air anyway, and 3/4 of the year they hardly need any heating.

Just do the sums.

[Gill]

10 hours ago, JohnMo said:

Most UK manufacturers seem to do custom cylinders if you want them.  So you could in effect have any number of immersion heaters at different levels.  So you could for instance, have E7 one dedicated, have one at a high level for not so sunny days, this would then move to the a lower one once the top is satisfied on a really sunny day.

 

@Nickfromwales go to place seems to be Trevor at cylinders2go.  So it may be worth having a discussion direct with them, other suppliers are available.

 

Thanks for that info. Sounds like that could fit my needs. I'm probably being daft but on a sunny day I'm thinking the E7 would have got the tank to temp overnight and the solar would purely be doing top up of heat losses.

In such a situation I'm guessing that I need to be monitoring the weather and then deciding if I want any water being heated overnight. 

[Gill]

10 hours ago, SteamyTea said:

The biggest changes will be reducing water usage, will over shadow everything else.

I think my water use figures are probably a bit high. 

Current worst case, two short shower (5 mins) , maybe two basins of water for dishes and a bucket or two if hot water if the floors are getting washed. 

The bathroom remodel is going to bring in a replacement bath (deep soaking tub) that can take about 200 litres. It's a luxury but our current bath is bigger and needs so much water that it's never used. I miss a soak. 

[JohnMo]

46 minutes ago, Gill said:

 

Thanks for that info. Sounds like that could fit my needs. I'm probably being daft but on a sunny day I'm thinking the E7 would have got the tank to temp overnight and the solar would purely be doing top up of heat losses.

In such a situation I'm guessing that I need to be monitoring the weather and then deciding if I want any water being heated overnight. 

I would think of it the other way round.

 

On a sunny day your cylinder temp will be high by the end of the day, so will not need heating by E7 overnight. Size and operate for the same temps as a heat pump.  So use E7 to keep the cylinder as 50 to 55 size at 300l plus.  Set the other immersions to heat to max temp the cylinder allows.

[Gill]

8 hours ago, SteamyTea said:

I don't think it would, at worse, be worse than resistance heating.

Houses need to expel air anyway, and 3/4 of the year they hardly need any heating.

Just do the sums.

 

 

We started with the heating in November and its still on this month so we're closer to half the year. Hopefully we'll cut this as sort out the place. 

 

I do need to do some sums on ESHP and see what the scop would be if it draws from outside. Not sure how to calculate the heat reduction if draws from internal. I know that they can integrate with pv but not sure how using off peak eco 7 would work. 

[Nickfromwales]

2 hours ago, JohnMo said:

I would think of it the other way round.

 

On a sunny day your cylinder temp will be high by the end of the day, so will not need heating by E7 overnight. Size and operate for the same temps as a heat pump.  So use E7 to keep the cylinder as 50 to 55 size at 300l plus.  Set the other immersions to heat to max temp the cylinder allows.

Yup. +1. 

[SteamyTea]

38 minutes ago, Gill said:

We started with the heating in November and its still on this month so we're closer to half the year

Yes, but some days it is hardly adding any energy.  Not as if every winter day is -5°C.

I have fully turned mine off now, starting to think I have have been a bit early as house is only at 18°C, but it is only 6.6°C outside now, and has been for the last two hours.

[Gill]

5 minutes ago, SteamyTea said:

Yes, but some days it is hardly adding any energy.  Not as if every winter day is -5°C.

I have fully turned mine off now, starting to think I have have been a bit early as house is only at 18°C, but it is only 6.6°C outside now, and has been for the last two hours.

We're at 18 ish with heating (35 Kwh) yesterday. Tomorrow and Saturday is due to be sunny 13 degree peak so I've turned the storage off and will see what the house temps do. Hopefully the sun room will get up to around 26 and we take some of that heat into the main house. 

[SteamyTea]

13 minutes ago, Gill said:

Tomorrow and Saturday is due to be sunny 13 degree peak

11°C peak tomorrow, about the same as today.

May get some sun tomorrow afternoon.

Trouble is sea surface temperature and air temperature are very similar, so may be misty instead.

 

[Gill]

35 minutes ago, SteamyTea said:

11°C peak tomorrow, about the same as today.

May get some sun tomorrow afternoon.

Trouble is sea surface temperature and air temperature are very similar, so may be misty instead.

 

Same situation at my wee caravan on the ayrshire coast. Does make for some splendid Ailsa Craig sunsets mind you. One day I might feel confident enough to build out an all year place there but plenty learning to do before that's feasible. 

[Gill]

On 06/04/2023 at 12:04, SteamyTea said:

I don't think it would, at worse, be worse than resistance heating.

Houses need to expel air anyway, and 3/4 of the year they hardly need any heating.

Just do the sums.

Finally got round to doing some sums. 

 

Water heating currently around 6kWh daily so with a bit of round up call it 2500 annual. 

 

Eshp with a cop of 2.5 would mean a 1500kWh a year reduction saves £225 at my current overnight rate of £0.15 

 

Hopefully these models make firya reasonable comparison. 

 

ESHP (Vaillant aroSTOR 270) - £2300

Telford Tempest 300  Indirect Unvented Cylinder TWIN Immersion - £750

 

So about a 7 year payback assuming identical maintenance costs between both systems. I've not looked at install cost differences. 

 

The Telford states lifetime guarantee (I'm sure there are exclusion). The ESHP 5 years on the cylinder and 2 on other components. 

 

Adding solar to the mix increases the payback time on the ESHP and I can't help but assume an unvented cylinder will be a cheaper product for repair /maintenance. 

 

Unless my maths is way off, looks like UVC with multi immersion is the way to go. 

[RichardL]

1 hour ago, Gill said:

Unless my maths is way off, looks like UVC with multi immersion is the way to go. 

Certainly good enough for me to measure my own actual immersion spend on DHW before making a decision...

Very much evens depending on your optimism re energy prices (will always go up shortening the gap),
how long off peak overnight will last (finite and require more automation vs. time windows to access),
and reliability of equipment ?  - who knows - luck? (I don't hold much faith in warranties TBH)

-but- if the ESHP does last 7 years (or less as prices go up) after that its all downhill and that 2020 hindsight will be looking over your shoulder.

Edited April 8, 2023 by RichardL

[SteamyTea]

1 hour ago, Gill said:

Water heating currently around 6kWh daily so with a bit of round up call it 2500 annual. 

 

Eshp with a cop of 2.5 would mean a 1500kWh

Would be 1,000 kWh

[1/2.5 * 2,500).

So

Saving = (2,500 x 0.15) - (1000 x 0.15) = 225

So that bit was right.

 

EASHP After 5 years

 

(2,300 + 150) / 5 = 490 £/year

 

UVC after 7 years

 

(750 + 375) / 7 = 160 £/year

 

 

It is the dilemma I have had for years.

My power bills are just too small to change anything.

 

Edited April 8, 2023 by SteamyTea

[Gill]

12 minutes ago, RichardL said:

if the ESHP does last 7 years (or less as prices go up) after that its all downhill and that 2020 hindsight will be looking over your shoulder.

 

16 minutes ago, RichardL said:

Certainly good enough for me to measure my own actual immersion spend on DHW before making a decision...

Very much evens depending on your optimism re energy prices (will always go up shortening the gap),
how long off peak overnight will last (finite and require more automation vs. time windows to access),
and reliability of equipment ?  - who knows - luck? (I don't hold much faith in warranties TBH)

-but- if the ESHP does last 7 years (or less as prices go up) after that its all downhill and that 2020 hindsight will be looking over your shoulder.

 

I can see time of use tarrifs becoming far more prevalent with the EV use case. Not sure what that means for Eco7 style tarrifs. Really do need a crystal ball for this stuff! 

 

There's a part of me that wants ESHP to be the solution but the savings aren't dramatic enough to accept the risk of maintenance /repair on 2.5k system (that few plumbers up my way have the faintest idea about). 

 

I'll expect a tap on the shoulder from hindsight in 2030. 😁

 

 

 

 

[Gill]

41 minutes ago, SteamyTea said:

EASHP After 5 years

 

(2,300 + 150) / 5 = 490 £/year

 

UVC after 7 years

 

 

(750 + 375) / 7 = 160 £/year

52 minutes ago, SteamyTea said:

 

 

 

 

Should that not be 

(2,300 + (150*5)) / 5 = 610 £/year

(750 + (375*7)) / 7 = 482 £/year

 

I prefer you numbers on my pocket mind you. 

 

Agree that for smaller usage the outlay is hard to justify. If we were chewing through more DHW then I'd be more inclined to consider ESHP. 

 

[SteamyTea]

5 hours ago, Gill said:

Should that not be 

Yes it should be.

It was late.