Sunamp as a backup to a small DHW cylinder

[doyled]

Am keen to install a heat pump however siting a cylinder and buffer tanks is a problem - lack of physical space. The best I can look at is a 100 litre (vertical) or 150 litre (horizontal) cylinder. With a 150 litre horizontal cylinder I'm really pushing space constraints except if I can put the 3x buffer cylinders in another cupboard by the water riser about 4 metres away from where I want the cylinder.

 

My question is whether anyone has ever used a Sunamp as a backup to a normal cylinder? There are just 2 of us in the house and our normal water consumption requirements should be able to be serviced from a 100 litre approx vertical cylinder, but I appreciate this just won't be enough for other occasions such as having a bath.

 

I'm awaiting my installer (Evergreen) to do a site visit to discuss siting options, however I am wondering if there's a way to pipe in a small Sunamp as a backup for those odd times when more than 100 litres of hot water is required - so most of the time the cylinder would refill with cold water but for odd occasions for heavy hot water demand it could be plumbed to pull hot water from the Sunamp instead, which would then be recharged after.

 

Is this even a viable option though.....?

 

Thanks,

 

David.

[joth]

Are you heating it from gas boiler, ASHP, oil, direct electric, other?

 

I think for 2 ppl in a space constrained situation, if you're doing sunamp at all the only sensible choice would be to get the largest sunamp you can and forgo the cylinder. The only drawback of that is if you're hoping to charge it from ASHP, but you have that issue anyway.

 

Alternatively, if you're not using ASHP (or can compliment it with anything else), the easiest way is to increase capacity of a UVC is to increase the storage temperature. E.g. you can store water at 50 deg C most the time, but bump it up to 85 on the days when you know you need more. We do this with ASHP and the immersion heater as a boost to get above 55 deg C.  (I have it all automated, so the more people staying in the house overnight, the hotter the tank is in the morning, charged up from overnight cheaprate electric). 

In case it's not obvious, this depends on having thermostatic mixer on the outlet / all showers, so that a constant temp is delivered, but using less DHW from the tank if t's at a higher temp, thereby achieving a larger effective heat energy store.  

You can't do this with Sunamp, hence why UVC is strictly better for "variable storage" requirements. 

 

 

btw if you mostly use DHW for showers, you can reduce their demand by about 35% by installing a showersave.com device.

Also if you're having a boiling water tap in the kitchen you can consider getting one with an integrated instant DHW supply (e.g. Quooker Combi) which also reduces demand on the main tank

Edited January 18, 2022 by joth

[ProDave]

1 hour ago, doyled said:

I'm really pushing space constraints except if I can put the 3x buffer cylinders in another cupboard

What are these THREE buffer cylinders?  That seems to be the issue if you are short on space?

[doyled]

6 minutes ago, ProDave said:

What are these THREE buffer cylinders?  That seems to be the issue if you are short on space?

 

This is what the installer sent me. I'm pretty baffled also. My issue is that I can - at a squeeze - I can put in a large tank but these extra elements are a killer. I just don't have a large spare cupboard to host all this.

[doyled]

51 minutes ago, joth said:

Are you heating it from gas boiler, ASHP, oil, direct electric, other?

 

I think for 2 ppl in a space constrained situation, if you're doing sunamp at all the only sensible choice would be to get the largest sunamp you can and forgo the cylinder. The only drawback of that is if you're hoping to charge it from ASHP, but you have that issue anyway.

 

Alternatively, if you're not using ASHP (or can compliment it with anything else), the easiest way is to increase capacity of a UVC is to increase the storage temperature. E.g. you can store water at 50 deg C most the time, but bump it up to 85 on the days when you know you need more. We do this with ASHP and the immersion heater as a boost to get above 55 deg C.  (I have it all automated, so the more people staying in the house overnight, the hotter the tank is in the morning, charged up from overnight cheaprate electric). 

In case it's not obvious, this depends on having thermostatic mixer on the outlet / all showers, so that a constant temp is delivered, but using less DHW from the tank if t's at a higher temp, thereby achieving a larger effective heat energy store.  

You can't do this with Sunamp, hence why UVC is strictly better for "variable storage" requirements. 

 

 

btw if you mostly use DHW for showers, you can reduce their demand by about 35% by installing a showersave.com device.

Also if you're having a boiling water tap in the kitchen you can consider getting one with an integrated instant DHW supply (e.g. Quooker Combi) which also reduces demand on the main tank

 

This is a great suggestion, thank you. So simple I feel stupid for not even thinking about this. I was looking at some online calculations around a typical split of hot/cold water temperature. Looking at a 250 litre bath gives 40 degrees final mixed temp with a mix of 100 litres hot water at 85 degrees and 150 litres cold at say 10 degrees. 

 

I have a combi gas boiler at present. I was wanting to go for a Midea ASHP for DHW and heating. 

 

Using immersion and/or bumping up the ASHP temporarily feels like a far more sustainable option then buying additional kit that will just sit there unused for much of the time.

 

I'm hoping to add solar heat / PV at a later time so would look to get a twin coil cylinder with immersion to give options for future.

[ProDave]

I am confused from the picture.  What is the big black tank if it is not your HW tank?

 

The things on the wall are expansion vessels they can move much higher to make more space.

 

Is that picture new as in work in progress or what you have had for some time?  Plenty of room in that cupboard if it was laid out properly.

[doyled]

38 minutes ago, ProDave said:

I am confused from the picture.  What is the big black tank if it is not your HW tank?

 

The things on the wall are expansion vessels they can move much higher to make more space.

 

Is that picture new as in work in progress or what you have had for some time?  Plenty of room in that cupboard if it was laid out properly.

 

This is an example layout as provided by the installer from another customer. It was to show me that there would be a number of others physical items to accomodate than just the cylinder itself. So not my cupboard I'm afraid....!

 

The only siting location I realistically have is under the landing area / lower set of stairs down to my kitchen. 

 

 

I'd love to have a big cupboard elsewhere in the house with an existing cylinder and paraphernalia but I just don't. Here is the current plan view of this area.

 

 

I need to have a new downstairs toilet so this will be fashioned out of the existing understairs cupboard area by extending the walls out. This then leaves the area under the landing and the area under the stairs from the landing to the kitchen for storage. I wanted to use some of that space for a cylinder and piping. Here's an example of the layout I was hoping for, using either a horizontal tank or vertical tank.

 

 

I looked at World Heat Cylinders to get some dimensions and see what might be able to fit, then modelled this to the understairs area available.

 

 

These are of course very tight fits! But would make good use of difficult to use storage areas.

 

My builder is removing the lower set of stairs and the landing area so access should be ok for install.

 

If the expansion vessels can be accomodated somewhere close to the cylinder this may also be a potential option, as there is another storage area by the water riser.

 

Based on the advice above from joth I think I'm now keen on a 100 litre vertical cylinder, which looks to be an easier option to install together with expansion vessels and avoids stratification issues with a horizontal. 

 

I expect that this may seem like absolute fantasy to achieve, but this is the only way I can realistically change from combi gas to ASHP - either by locating the cylinder here or by using a separate Sunamp for DHW which could be accomodated in a small upstairs cupboard that is too small for a cylinder.

Edited January 18, 2022 by doyled

[JohnMo]

I would just bite the bullet and use a single Sumamp.  Anything else is just p***ing about if you are going ASHP, with your space constraints.  The other is install cylinder in loft space, if you have one.

 

Or stay with gas.  And wait for high temperature heat pumps to come available.

 

[joth]

8 minutes ago, JohnMo said:

I would just bite the bullet and use a single Sumamp.  Anything else is just p***ing about if you are going ASHP, with your space constraints. 

 

The irony being, if you are using an ASHP the Sunamp requires even more p***ing about, last I looked .. ?

 

1 hour ago, doyled said:

Looking at a 250 litre bath

That's a very large bath. If that's the actual size, and you expect to use it regularly, you maybe just as well to keep the combi boiler.

[Mr Punter]

Another vote here to stick with the combi.  Spend the money on better insulation and airtightness.

 

If the motivation for the ASHP is to be more environmentally friendly, perhaps fewer baths or look at fitting waste water heat recovery instead.

[Gone West]

6 hours ago, doyled said:

There are just 2 of us in the house and our normal water consumption requirements should be able to be serviced from a 100 litre approx vertical cylinder, but I appreciate this just won't be enough for other occasions such as having a bath.

While we were building our last house we lived in an old bungalow with a 90l vented hot water tank which was tall and slim. We heated the water to 70C with an oil fired boiler and had baths. By the time the bath was finished the tank had heated up again.

[SteamyTea]

6 hours ago, joth said:

but bump it up to 85 on the days when you know you need more

Don't cylinders have a thermal cut out at 65⁰C now. The one at work does, and think mine, at home  does as well.

[joth]

1 hour ago, SteamyTea said:

Don't cylinders have a thermal cut out at 65⁰C now. The one at work does, and think mine, at home  does as well.

Looks like the immersion on mine will go to 70ºC +/- 5ºC, and has a second cut out at 87ºC, and the UVC T&P valve fires at 90.

https://osohotwater.co.uk/wp-content/uploads/2021/11/Manual-Delta-Geocoil-DGC-UK.pdf

So yep 70 maybe a more reasonable max target. 

 

[doyled]

So it looks like a World Heat cylinder can be used with immersion heaters with a cut out up to 95 degrees can be used, though I suspect running below that would be best.....

 

I checked my bath again and the dimensions do indicate it would be around 250 litres of water to take it to the level I normally fill it to, but I like it super full when I get in. Looking at an online calculator https://www.onlineconversion.com/mixing_water.htm and putting in the following figures gives a final temperature of 40 degrees. 

 

100 litres @ 85 degrees C

150 litres @ 10 degrees C

 

So I suspect this might be quite tight for comfort.... likely need another 15-20 litres of hot capacity perhaps.

 

Thanks for all the input.

 

[dpmiller]

^ I can confirm that the stat on the Tesla heaters in our World Heat tank maxes out at  around 92c