Tank Sizes

[Nickfromwales]

Yup direct is a no no if that's the case. 

TS does require an EV just the same. If you're just needing dhw then an uvc will suffice. Do you have Ufh?

[DeeJunFan]

UFH and DHW.

 

[Nickfromwales]

How are you heating the Ufh?

this is where we miss EB. No ability to review members' content.

[jack]

Has anyone let the Sunamp guys know about the new forum?

[DeeJunFan]

I was thinking of running the whole show off the one tank.

So UFH & DHW from the same tank.  I have no idea of the volume of water that would go through the UFH system, and the hotpress plumbers over here aren't keen on consultations.

This was a thread i had started on the Pro/cons of ASHP over Immersion

http://www.ebuild.co.uk/topic/18673-ashp-or-immersion/page__hl__deejunfan

I'm keeping an eye on the ASHP scenario for a possible bargain, but was going to see how things went going straight direct electric for both UFH & DHW with the PV as additional input.

I had done another thread on possible setup but cant find it now.

I'm happy enough to add a 12kw in-line booster as Jeremy has and also some In-line heaters at wash hand basins to reduce DHW demand and dead legs.

So fingers crossed 500L would be enough.  And it wont cost a fortune to heat the water!

[Nickfromwales]

1 hour ago, jack said:

Has anyone let the Sunamp guys know about the new forum?

Pop that in the mod section mate.

[reddal]

Hi,

What temperature are you planning to keep the thermal store at?

I initially had problems because my installer didn't realise that thermal stores aren't good at providing hot water when kept just a bit above the target hot water temp.

Some discussion from the old site :

Quote

Hi,
 

Quote

Nickfromwales, on 01 October 2013 - 09:07 PM, said:

First up, what is the capacity of the thermal store?

The thermal store is 300L.
 

Quote

Nickfromwales, on 01 October 2013 - 09:07 PM, said:

Its possible that your system designer f****d up big time and should have installed a whopper, or multiples of these.

Yes - the thermal store should have been a lot bigger. The original design had just the 300L thermal store. The installers who designed the system thought this would be plenty - and 300L is a lot of hot water - but they didn't understand that a thermal store doesn't work like a traditional hot water cylinder - it starts losing temperature immediately - compared to a cylinder which gives you most of its capacity at its initial temperature - then quickly drops to the input temperature. Here is a simulation I did to illustrate that :



Because the GSHP only gives hot water at 50c - the output only has to drop 5c or so before its not really hot enough as domestic hot water. This meant we didn't even get a single full bath of hot water from the system!

A thermal store has the same total amount of energy in it as a normal cylinder - it just outputs that energy at a different rate. If the thermal store had been much bigger - or we had a primary heat source that provided much higher temperatures there would have been less of an issue. However it became clear that them specifying a 300L thermal store with a GSHP as primary source was a mistake.

...

- reddal

 

Edited May 26, 2016 by reddal

[PeterW]

I've got a 500L UVC from Trevor with a HP coil and it has a single immersion. The HP coils are different as they are high recovery and circa 3sqm IIRC

It is pretty big but the issue we had was the 60 litre floor standing EV..! That is definitely one for the attic if you go for a UVC. Also be aware that the control group they provide is 28mm and is a serious bit of kit that needs planning in.

Price was in line with what Nick quoted

 

 

 

DOC230216.pdf

[DeeJunFan]

I have been doing some cost calcs based on a set temp of 60.  But i'm not sure what amount of recharge may be required

[reddal]

1 hour ago, DeeJunFan said:

I have been doing some cost calcs based on a set temp of 60.  But i'm not sure what amount of recharge may be required

If my calculations are correct (they might not be!) - a 500L thermal store at 60c would deliver about 260L of water with the mixer set to 45c - before the temp started to drop below that level. That sounds ok - enough for a couple of baths/showers at least before the temp starts getting tepid. If you want the output temp to be mid 50's though then you would get less than 100L before it drops below that level.

Others can comment with more authority than me on if 500L at 60c gives enough capacity. It sounds to me like it would - but is a little bit tight.

A thermal store for DHW would perform a lot better if at a higher temp - like 75c.

- reddal

ps a graph :

 

Edited May 26, 2016 by reddal
Add graph

[DeeJunFan]

That sounds not too bad - out of interest how does one calculate such a thing?

260L would likely struggle to cope with UFH and DHW

I would be happy enough going up to 75.  

At that rate trying to do anything with an ashp would be merely a pre-heat unless i could go for a much bigger tank, which at this stage i can't

I wonder should i just accept it and take the hit on higher price for direct electric heating, but lower capital outlay.

We are having a stove so perhaps an idea would be to go for a stove with boiler for cover all situations.  eg

https://www.stovesonline.co.uk/wood_burning_stoves/Woodfire-CXT12-boiler-stove.html#entity_8266

D

[reddal]

7 minutes ago, DeeJunFan said:

That sounds not too bad - out of interest how does one calculate such a thing?

I was just doing a very simple simulation - assuming no losses etc. ie for each liter of water calculate how much would be drawn from the tank (given the mixer trying to get eg 45c) and work out how much energy this removes from the tank - and what the remaining temp of the tank would be. And I might have done it wrong... though I can tell you from experience that the reality is something along these lines.

Quote

260L would likely struggle to cope with UFH and DHW

Yes I would guess that a thermal store at 60c might struggle to deliver enough hot water if it was also running the heating. e.g. you heat the store up to 60c - then the UFH kicks in and draws heat from the store pulling it down to 50c - and then you will wont have enough hot water for a bath before the store is below 45c.

 

Quote

At that rate trying to do anything with an ashp would be merely a pre-heat unless i could go for a much bigger tank, which at this stage i can't

If DHW and UFH are both working off the same store - which is pre-heated by ASHP - but you want the DHW to always be available - then be careful because its easy to end up not using the ASHP at all for the UFH - and essentially just using (expensive) electric heating. i.e. if the ASHP can heat the tank up to 45c - but the immersion heater kicks in before this then the immersion heater will power the UFH. Alternatively the immersion heater can be linked to the ASHP and doesn't come on until the ASHP has been given a chance to contribute (ie tank down the 30c) - but then there will be plenty of times when you effectively don't have DHW available!

We struggled with these issues and ended up with a seperate DHW cylinder and thermal store - however its a bit of a compromise.

Others here are more expert on this stuff than me and can comment more authoritatively.

- reddal

[Nickfromwales]

Ok. 

Separate the dhw and space heating, using a small buffer for the heating, with an immersion as a failsafe ( designed to run off grid electric ) and an UVC for dhw. 

Tell your missus that your going out for some milk, then go buy a cheap ashp off eBay and bring it home. Lie and say it cost a fortune. Plumb for the ashp accordingly and use excess Pv to heat the UVC to target temp, say 65-70o and use the ashp to boost ( via the dedicated controls eg 55o flow for "hot water demand" only during the colder seasons where you get little or no solar gain.

Trying to run heating and hot water off electric via immersions is just not going to be a viable option IMHO, as dhw is the killer. Why run around putting inline heaters everywhere when a single solution for hot water is easily achievable, if sized and fed accordingly. At the very least I'd say you should go for an electric system boiler. Space heating should be negligible so the real problem here will always be dhw. Taking both out of a TS fed from electric though is, IMO, not going to end well. 

[PeterW]

Oddly this is where I am at with things at the moment and an ASHP that can do two different temperatures - 35c for UHF and 50c for DHW which is boosted by immersion / PV divert.

Using W-plan it ensures you've always got DHW priority, but that isn't for everyone !

[reddal]

4 minutes ago, PeterW said:

Oddly this is where I am at with things at the moment and an ASHP that can do two different temperatures - 35c for UHF and 50c for DHW which is boosted by immersion / PV divert.

So there are two different tanks - one for DHW and another for heating?

[DeeJunFan]

I'm getting more confused by the minute.

I'm averaging 5 hours sleep at night for the last few weeks so i could be just super stupid at the moment.

11 minutes ago, Nickfromwales said:

Ok. 

Separate the dhw and space heating, using a small buffer for the heating, with an immersion as a failsafe ( designed to run off grid electric ) and an UVC for dhw. 

Tell your missus that your going out for some milk, then go buy a cheap ashp off eBay and bring it home. Lie and say it cost a fortune. Plumb for the ashp accordingly and use excess Pv to heat the UVC to target temp, say 65-70o and use the ashp to boost ( via the dedicated controls eg 55o flow for "hot water demand" only during the colder seasons where you get little or no solar gain.

Trying to run heating and hot water off electric via immersions is just not going to be a viable option IMHO, as dhw is the killer. Why run around putting inline heaters everywhere when a single solution for hot water is easily achievable, if sized and fed accordingly. At the very least I'd say you should go for an electric system boiler. Space heating should be negligible so the real problem here will always be dhw. Taking both out of a TS fed from electric though is, IMO, not going to end well. 

Small Buffer? - How small is small 100L? 50? (I have no idea how much water UFH uses) with say 3kw Immersion 

Then UVC - should this be 500L or smaller?

When you say plumb accordingly do you mean ASHP to buffer, then buffer into UVC.  UFH circuits fed from buffer and excess from buffer fed to UVC

So most of the year the ashp would be heating to say 35-40 degrees, this would go to UFH and UVC pre-heat.  They top up the UVC with PV/Immersion. So i would still be heating DHW with direct electric (hopefully a lot of it "free" from PV) Would the savings from ashp pre-heat payback the expense of ashp and plumbing associated?

My head hurts!

 

[DeeJunFan]

14 minutes ago, PeterW said:

Oddly this is where I am at with things at the moment and an ASHP that can do two different temperatures - 35c for UHF and 50c for DHW which is boosted by immersion / PV divert.

Using W-plan it ensures you've always got DHW priority, but that isn't for everyone !

So Peter, 

You have an ASHP and an UVC with ASHP coil.  Do you also have a buffer tank?

Just to clarify W-plan is Water-Plan, this is a setting on your ASHP?

Thanks

 

[PeterW]

8 minutes ago, reddal said:

So there are two different tanks - one for DHW and another for heating?

Nope just DHW - volume of water in a decent UFH and the temperature rise you can get is small enough that you may not need a buffer as long as you don't have the hysterisis set too low and get it cycling. I'm looking at a buffer of no more than 70-100 litres assuming I can even get one that small as an option but I am not overly concerned about it 

[PeterW]

5 minutes ago, DeeJunFan said:

So Peter, 

You have an ASHP and an UVC with ASHP coil.  Do you also have a buffer tank?

Just to clarify W-plan is Water-Plan, this is a setting on your ASHP?

Thanks

 

W-Plan is a standard wiring plan as like S-Plan and Y-Plan, it just prioritises DHW over heating (see here W-Plan Link )

This is a rough schematic of what I plan to do here - it uses a 3 position valve output (via Orange wire) to switch the relay to sense either the 50c or the 35c sensor.

ASHP > Tank is the always open route, which means the auto bypass is only needed when the UFH is satisfied and the mixer valve closes down before the pump goes off.

NOTE - this is still being planned !!

[Calvinmiddle]

I have a gas combi so this isn't completely the same but I found I had to introduce a buffer tank to the heating side of the boiler as it wasn't able to module down low enough to run 25o water in the UFH pipes.  So I have a 70litre buffer tank that gets heated up, then when the house needs heat it draws it from it and when the temperature in the buffer tank drops then the boiler fired up to heat it up again

[Nickfromwales]

W plan hydraulically separates the flow from the heating and water. Eg when dhw is required the system takes that as number 1 priority. The 3-port diverter valve can ONLY supply one application at any given time ( on purpose / by design ) so the ashp can then toggle between low and high temp modes ( eg it knows it doing heating only so adjusts for that and vice versa for DHW ). 

The uvc will be heated to 50-55o ( user definable on the ashp ) so you'll not need to go much higher than that tbh with 500 Ltrs. The solar Pv will roof this to over 70o when generating so the ashp will only kick back in when the cyl stat calls for heat ( eg a bath drawn late evening ). Electric immersion can be manually set to stay off until boost is required ( then fed with grid electic ). The buffer is required to stave off short cycling and iirc also helps the ashp defrost by it pulling that water back through the ashp. More to follow when I get the last couple of 600x600 kitchen tiles down 

 

edited to add : the boost immersion would be immersion #2, with immersion #1 dedicated for Pv. Most Pv diverters will also have a boost button so in very adverse situations, you'll be able to push 6kw into dhw

[PeterW]

The slight difference in my setup is that normally a W-Plan uses a diverter valve which is in essence a 3 way valve with a spring return. It has only 2 wires (L/N) and is binary in its flow.

I've used a mid position valve for a couple of reasons - firstly I get feedback off the orange wire (240v when open) to drive a relay, and secondly I get the benefit of the time delay on opening (circa 8 seconds) that will allow the HP to start up and push the slug of cool water out and before the relay kicks over to the lower temperature. This would hopefully stop the issue of the HP kicking in then straight out as it would see "hot" water on the 35c stat. To drive it the same all I need is a signal on grey and white combined to open it.

Well that is the plan.... And it also reuses a brand new 3 port I happen to have lying around !