Design Help - Plumber not helping

[Declan52]

Just now, DeeJunFan said:

Were you there?

 

Yep Thursday night crawling around all sniper like around mayobridge is my normal routine. Hard to break old habits!!!

Don't worry my dearest called me all sorts of names during our build usually starting with what did you do that for you stupid ************.

[DeeJunFan]

Gotta love the stress of a self build!

[joe90]

11 hours ago, Declan52 said:

 

Don't worry my dearest called me all sorts of names during our build usually starting with what did you do that for you stupid ************.

 

My stance on this is my reply will be " if you can do better then be my guest!" ( knowing full well that my better half could not!)

[joe90]

DeeJunFan, have you finalised your plumbing design yet?

[DeeJunFan]

1 minute ago, joe90 said:

DeeJunFan, have you finalised your plumbing design yet?

 

By finished if you mean haven't really started then yes.

 

First plumber went off radar, then second plumber went off radar.  So my entire plan so far is on this thread.  

 

But in very general terms.  My understanding is 

 

ASHP Feeds low temp UFH tank (300l Buffer/TS)

ASHP Feeds DHW tank (300L UVC) at higher temp.  DHW is boosted by solar PV/Direct electric immersion 

 

DHW and UFH plumbed in a W Plan

 

According to @PeterW The design that came with my ASHP is not correct so i'm hoping i can get a drawing of what changes would need to be made.

 

@Nickfromwales has convinced me to keep it simple.

 

If i ever get speaking to an actual plumber face to face who is willing to take on my job i'm hoping they will understand what i'm on about.

 

 

[Guest Alphonsox]

You shouldn't need a dedicated UFH buffer tank anywhere near that size. The cost will be prohibitive as it need to be filled with expensive glycol (antifreeze). We are using a 90ltr buffer and that is only because I got a good deal on one. A 50ltr buffer should be fine.

 

Edit :- alternatively make sure the buffer has an indirect coil to limit the amount of antifreeze required.

[joe90]

Apart from the PV my plan is nearly the same. I will still probably go with the modulating in line heater as per JSH just to make sure I don't run out of hot water or tepid water is made hotter. I love the KISS principle. Jeremy,s blog shows how he designed a really technical way of controlling his heating and then changed his mind to a simple room stat. I hope you find a good plumber soon, I will be doing my own but I have a neighbour who is qualified and offered to look over my shoulder to make sure I don't cock it up completely. Keep us informed ?

[DeeJunFan]

31 minutes ago, Alphonsox said:

You shouldn't need a dedicated UFH buffer tank anywhere near that size. The cost will be prohibitive as it need to be filled with expensive glycol (antifreeze). We are using a 90ltr buffer and that is only because I got a good deal on one. A 50ltr buffer should be fine.

 

Edit :- alternatively make sure the buffer has an indirect coil to limit the amount of antifreeze required.

 

There you go i had no idea there was a requirement for anti-freeze.  You learn something new everyday.  

 

Does anyone want to buy a house?  First fix electrics are done!  Plumbing not started.

[Nickfromwales]

Antifreeze + inhibitor, a combined product, and its diluted not concentrate. . 

51 minutes ago, Alphonsox said:

You shouldn't need a dedicated UFH buffer tank anywhere near that size. The cost will be prohibitive as it need to be filled with expensive glycol (antifreeze). We are using a 90ltr buffer and that is only because I got a good deal on one. A 50ltr buffer should be fine.

I've suggested a bigger buffer and to make it a TS to get cold mains uplift from the ashp via a internal DHW coil. The reason for the larger size is to get max yield from the low grade / good CoP in order to return the lowest DHW running costs. Pv to HP when running, and excess diverted to UVC when available. 

If the HP is running in the winter when pv tails off / stops then DHW will be the biggest consumer of energy, so the idea is to use ~35-38oC HP flow to provide around 3/4 of the DHW energy, rather than use the higher temp / poor, zero or negative CoP direct to the UVC for DHW. 

I ( have ) stated that the sizing be respective of the property, occupants and expected ( future anticipated ) consumption, and patterns. 

 

52 minutes ago, Alphonsox said:

Edit :- alternatively make sure the buffer has an indirect coil to limit the amount of antifreeze required.

The coil in a small tank would likely struggle to indirectly transfer the heat from the HP to the DHW uplift coil in such a small vessel, at the rate it could be consumed, so again reinforces my suggestion of a larger buffer ( TS ) . 

 

Maybe I'll call Telford and see what the coils can actually do, but my gut says bigger is better here. It's no real extra cost on installation other than twice / three times the volume of antifreeze and a few hundred on the larger tank ( remembering it would have a DHW coil costed in either way ). If we're on the right track I can get some exact details which would allow me to be firmer on the cylinder types, and sizes. 

Let me get out of these wet clothes and into a dry martini and I'll come back with the outcome . 

Focker out. 

[DeeJunFan]

49 minutes ago, Nickfromwales said:

Antifreeze + inhibitor, a combined product, and its diluted not concentrate. . 

I've suggested a bigger buffer and to make it a TS to get cold mains uplift from the ashp via a internal DHW coil. The reason for the larger size is to get max yield from the low grade / good CoP in order to return the lowest DHW running costs. Pv to HP when running, and excess diverted to UVC when available. 

If the HP is running in the winter when pv tails off / stops then DHW will be the biggest consumer of energy, so the idea is to use ~35-38oC HP flow to provide around 3/4 of the DHW energy, rather than use the higher temp / poor, zero or negative CoP direct to the UVC for DHW. 

I ( have ) stated that the sizing be respective of the property, occupants and expected ( future anticipated ) consumption, and patterns. 

 

The coil in a small tank would likely struggle to indirectly transfer the heat from the HP to the DHW uplift coil in such a small vessel, at the rate it could be consumed, so again reinforces my suggestion of a larger buffer ( TS ) . 

 

Maybe I'll call Telford and see what the coils can actually do, but my gut says bigger is better here. It's no real extra cost on installation other than twice / three times the volume of antifreeze and a few hundred on the larger tank ( remembering it would have a DHW coil costed in either way ). If we're on the right track I can get some exact details which would allow me to be firmer on the cylinder types, and sizes. 

Let me get out of these wet clothes and into a dry martini and I'll come back with the outcome . 

Focker out. 

 

Again light clicks on,

 

So even though we are going with W plan you are still suggesting to max out the potential of the low temp tank and use it for cold water up-lift.  I was thinking that approach was to be abandoned.  

 

I didn't know you were a martini man!  all that talk of fire, meat and beer!

 

Really appreciate your help!

[Declan52]

Good plumbers here are like unicorns. Often spoke of and some surely exist but i still haven't found one. 

 

[Guest Alphonsox]

1 hour ago, Nickfromwales said:

Antifreeze + inhibitor, a combined product, and its diluted not concentrate. .

 

Thermox FCX seems to be around £190 (ex VAT) for 25Lts and needs to be diluted at 25%, so £570 for a 300Ltr buffer tank plus whatever the UFH and ASHP volume is.

[Dudda]

8 minutes ago, Alphonsox said:

 

Thermox FCX seems to be around £190 (ex VAT) for 25Lts and needs to be diluted at 25%, so £570 for a 300Ltr buffer tank plus whatever the UFH and ASHP volume is.

That's more expensive than I thought. How often do you need to replace or top up that on average?

[PeterW]

Hence my thought of using a cheap indirect 900x450 tank as a buffer and only running  the antifreeze in the supply circuit, split between the buffer and the DHW tank which means I would be running about 15 litres in the circuit but the down side is I don't think that's enough to keep the ASHP happy but could be wrong as I've got one running 12m of 28mm on to a Telford HP tank and it doesn't complain.  

 

Question then is what is the minimum head or pressure UFH can work at ..?? I would have 90 or so litres of buffer no more than 1m above the floor (and probably 500mm above the circ pump) if I left the tank basically as an open vented tank. Thoughts @JSHarris..?

[le-cerveau]

Surely what you need is a dual coil tank, something like this (example picture):

Plumb the ASHP into the coil (shown on the left).

DHW pre heat on the DHW coil (for the shower head read feed into UVC).

UFH off the tank taps (radiators on the picture)

limits the anti freeze in the UFH system.

Reduces the DHW legionella issue as it is only the coil and separates it from the UFH so you can have inhibitor in the UFH circuit.

[Declan52]

Aren't most TS multi coiled. Mine has 1 for dhw, 1 for ufh, 1 for rads upstairs, 1 unused as i was originally going down solar thermal but gladly went pv.

[Nickfromwales]

9 minutes ago, DeeJunFan said:

I didn't know you were a martini man!  all that talk of fire, meat and beer!

Nah, just what I say when I start the day in 'clean' clothes, and then have to go back home to chuck the boots and combats back on 

 

11 minutes ago, DeeJunFan said:

 

So even though we are going with W plan you are still suggesting to max out the potential of the low temp tank and use it for cold water up-lift.  I was thinking that approach was to be abandoned.  

Well, before this got to a point where we assumed anything, and then you acted upon it, I thought it best to chat briefly with the tech guys at Telford to see what can actually be extracted from a X sized buffer tank with regards to DHW uplift via an instantaneous coil of X size. Bigger of both = more and vice versa. 

So....after a chat and a brew....deep breath...."options" :-

 

On the assumption that,

• You already will have an ashp installed and working. 
• You already will have a buffer of whatever size installed, according to majority advice and positive feedback here ( against running a HP to Ufh directly in a 'low' energy home ). 
• You will have a reasonably sized Pv array. 

I have arrived at the following :-

 

The costs of the larger buffer tank, having it fitted with a 4.5m2 DHW uplift coil ( the minimum size that would offer any meaningful yield at low temp but also physically too big to go into any less than a 300L cylinder ), accepting a reduced max flow rate of 18litres per min, ( you may well only have 18litres per min coming in so case specific for that point ), and the additional volume of antifreeze ( plus replacment of the antifreeze every 5 years as it has a limited working life ), make the TS and coil option for DHW uplift very tight, if not plain uneconomical for your expected DHW needs. 

 

So, after more head scratching, further tea drinking and procrastinating.....

 

The figures do stack up quite well in favour of going for a small buffer and copying @JSHarris with a plate heat exchanger, but as your expected DHW consumption and flow rates may well be double his, I'd suggest going for a pair of 30kw versions running in parallel to get a combined pipe size input & output of 22mm ( to match the UVC accordingly ). PHE example only

PHE's are far better at transferring heat from a wet source than coils, especially when being used at lower temps. I've had to adjust my thinking accordingly for this case, and even so, I still think it's a worthwhile endeavour. 

 

• Less long term labour of the ASHP = longer life expectancy. 
• Far fewer defrost cycles compared to driving DHW directly from the ASHP at high temp range. 
• Majority of the DHW getting produced at the better CoP rate, ( DHW will be your biggest energy requirement as its needed year round eg also when you have little or no Pv gain ). 
• Smaller buffer tank ( circa 100 litres ) with less loss, size, and reduced antifreeze required. ( thanks @Alphonsox for the example costs, makes it a game changer tbh ). 

So, to summarise, I'm still thinking of DHW uplift from the ASHP via a buffer, but a smaller buffer and PHE's instead of the coil. That will require a pump and flow switch, ( any PHE will need one ). Still relatively straightforward tbh, and may just provoke me into getting off my arse and looking for a decent plumbing schematic software so I can translate this babble into a working drawing for a / your plumber to follow. 

 

 

12 minutes ago, le-cerveau said:

Surely what you need is a dual coil tank, something like this (example picture):

Plumb the ASHP into the coil (shown on the left).

DHW pre heat on the DHW coil (for the shower head read feed into UVC).

UFH off the tank taps (radiators on the picture)

limits the anti freeze in the UFH system.

Reduces the DHW legionella issue as it is only the coil and separates it from the UFH so you can have inhibitor in the UFH circuit.

 

Thats the chat I've just had. These cylinders have very low heat transfer rates at low temp, so that type of cylinder would need to be VERY hot in order to do what is suggested in that image . It would also need to be KEPT very hot to do it too . 

[Nickfromwales]

2 minutes ago, Declan52 said:

Aren't most TS multi coiled. Mine has 1 for dhw, 1 for ufh, 1 for rads upstairs, 1 unused as i was originally going down solar thermal but gladly went pv.

You get them specific to your remit . No such thing as a "standard" TS afaik. 

[Nickfromwales]

3 hours ago, Declan52 said:

Aren't most TS multi coiled. Mine has 1 for dhw, 1 for ufh, 1 for rads upstairs, 1 unused as i was originally going down solar thermal but gladly went pv.

What did your plumber do with the unused coil tappings?

If they're left open you can get condensation forming inside and that causes corrosion. Not a prob if they're stainless, but if they're copper then they need sealing with a bit of foam / mastic. Don't cap them as there could be expansion issues with the coil heating and cooling the air inside. 

[Declan52]

Expanding foam and then a screwed cap i think. Knowing them probably what ever days paper it was cut up and shoved in.

[Nickfromwales]

12 minutes ago, Declan52 said:

Expanding foam and then a screwed cap i think. Knowing them probably what ever days paper it was cut up and shoved in.

[Jeremy Harris]

6 hours ago, Dudda said:

That's more expensive than I thought. How often do you need to replace or top up that on average?

 

 

The MIs say flush and replace every five years.  Adds a fair bit to the running cost, which is one reason I went for a low volume coil in a 70 litre, low temperature buffer tank, so I could just about get away with 10 litres of antifreeze/inhibitor concentrate (our total primary circuit volume is just over 40 litres).

[Guest Alphonsox]

Just a thought .... Are there any alternatives to (poly)ethylene glycol as an antifreeze agent for areas which don't drop far below freezing ? At the prices quoted Austrian wine would be cheaper.

[Jeremy Harris]

1 hour ago, Alphonsox said:

Just a thought .... Are there any alternatives to (poly)ethylene glycol as an antifreeze agent for areas which don't drop far below freezing ? At the prices quoted Austrian wine would be cheaper.

 

The problem is that heat pumps have a PRV that discharges to the environment, so the antifreeze/inhibitor has to be shown to have no adverse environmental impact and be non-toxic.  Ours would just pour the contents of the primary circuit out on to the ground underneath the unit if there was an over-pressure event.

[Guest Alphonsox]

2 minutes ago, JSHarris said:

 

... the antifreeze/inhibitor has to be shown to have no adverse environmental impact and be non-toxic.  

 

That rules out the local poitín I was considering