ASHP or oil boiler...

[Temp]

1 hour ago, Gone West said:

I'm hoping to do as you suggest but I was wondering about the oil boiler not being in condensing mode if the thermal store is heated to more than 70C. Does it matter?

 

The manual for our old Grant Vortex says the return to the boiler needs to be above 40C (to stop corrosion) and below 50C (to ensure condensing).

[Temp]

Our Grant Vortex feeds a 300L store and that feeds UFH and DHW.

 

The dial on our Grant boiler does not set the flow temperature, it sets the maximum flow temperature at which cycling will occur. What happens is the store calls for heat and the boiler fires up. The flow temperature starts rising until it hits the temperature set by the dial (which is unmarked). The burner (but not the pump) then shuts off and the flow temperature falls until the boiler decides to relight the burner. This cycling continues until the store is satisfied.

 

I found the best way to run it is to ensure the dial on the boiler is right up. Then crank up the boiler pump speed so that the flow temperature never gets hot enough to trigger cycling. The burner runs continuously until the store is satisfied. The pump has to be fast enough and the return temperature low enough so all of the power is sucked out of the boiler. If not the flow temperature rises until the dial limit is reached and cycling occurs.

 

I was recommended to fit a mixer in the boiler return so that the return is kept above 40C. This uses some of the boiler flow to heat the return but it only kicks in if the store is cold (eg after a holiday or first time heating is turned on).

Edited June 25, 2022 by Temp

[Gone West]

1 hour ago, Temp said:

Our Grant Vortex feeds a 300L store and that feeds UFH and DHW.

Thanks, that's useful info. So is your TS direct feed to the UFH or is there a heat exchanger in the store.

[Temp]

2 hours ago, Gone West said:

Thanks, that's useful info. So is your TS direct feed to the UFH or is there a heat exchanger in the store.

 

The same water goes through the boiler, into the store and out again to UFH manifolds. So no heat exchanger for the UFH. Although the water is the same, the two sides of the store are independent. If a room stat calls for heat hot water is taken from the top of the store and returned to the bottom. The boiler is controlled by a stat on the store and only fires up when the store cools enough.

 

This set up means every room can have/has its own stat/zone. No risk of the boiler cycling when just the bathroom UFH is calling for heat.

 

The above circuit is vented via a small expansion tank in the loft. This worries some people but hasn't been an issue. The circuit is dosed with Fernox F1.

 

There is a heat exchanger for the DHW. Mains pressure cold goes through an external heat exchanger on the store and off to the taps etc. In fact we have two heat exchangers, one is dedicated to a rather high flow rate shower. It's probably the best shower experience we've ever had. 

 

The heat loss from the thermal store, all the UFH manifolds and pumps is quite high. Would be an issue in summer if not in its own utility room. The TS could be better insulated.

Edited June 25, 2022 by Temp

[kommando]

3 years ago I DIY fitted a replacement oil boiler as the original 15 year old one had sprung a leak. The new one was a Hounsfield boiler, its condensing and the pipework was £20 over what came with the boiler, the oil pump on the burner is self priming so I could get rid of the Tiger loop I had before. I also reconfigured the flue from vertical to horizontal, this was the hardest bit as I had to drill through 2 ft granite wall with a rubble filled centre, get the hole done and then spend the next day feeding the flue through a hole that keeps changing size as the rubble moves around  . As for fossil fuel the burner is already burning HVO at Hounsfield under test with just some setting changes.  Total cost was £2000 including 2 160mm diameter diamond tipped boring heads, wore the first one out completely.

[Gone West]

13 hours ago, Temp said:

The TS could be better insulated.

Sorry for all the questions, but do you know the thickness of insulation on the TS. I've seen up to 100mm shown in adverts.

[PeterW]

1 hour ago, Gone West said:

Sorry for all the questions, but do you know the thickness of insulation on the TS. I've seen up to 100mm shown in adverts.

Newark Copper will custom make whatever you want including much thicker insulation. 

[HughF]

I’ve got a 500ltr buffer that needs to find a home, ex biomass install. Got loads of ports on it and it’s steel so you could easily weld on extra bosses as required. Drop me a Pm if that’s of any use. No coil in it though, obvs.

[Gone West]

1 hour ago, HughF said:

I’ve got a 500ltr buffer that needs to find a home, ex biomass install. Got loads of ports on it and it’s steel so you could easily weld on extra bosses as required. Drop me a Pm if that’s of any use. No coil in it though, obvs.

Thanks for the offer, but not what I'm looking for unfortunately.

[SteamyTea]

On 26/06/2022 at 08:14, Gone West said:

Sorry for all the questions, but do you know the thickness of insulation on the TS. I've seen up to 100mm shown in adverts.

Build it into a highly insulated and airtight cabinet.

 

[JohnMo]

Mine is 50mm which is way to thin, more the better.