Which heating and hot water solution(s) in 2024?

[Iceverge]

Interesting topic this one. 

 

I laboured over the best DHW solution for ages. Ended up at a direct 300l UVC, mostly because I was sick of all the sales nonsense and high capital outlay. It works fine and doesn't cost too much to heat. Hopefully very little whenever I put in some PV. 

 

On my plumbing research travels I became quite attached to the idea of Thermal stores. I subsequent installed a 250l maxipod thermal store in my parents house to merge an oil boiler and a solid fuel Rayburn to deliver pressurised hot water. It works really excellently. Instant hot water, no G3 or discharge pipework to worry about. 

 

However It needs to be kept at a high temperature to deliver any reasonable amount of DHW. Not ideal for an ASHP. 

 

You could just get a massive coil in tank TS (say 600l) and it'd work fine I bet. 

 

 

[Iceverge]

@dpmiller

 

Did you install the Harlequin Heatstream in the end? 

 

I really liked the idea but thought the storage volume too small. If they could make an really big one it would be ideal for an ASHP. 

[JohnMo]

1 minute ago, Iceverge said:

they could make an really big one it would be ideal for an ASHP. 

Big Red heat pumps used to do them. Spoke to Harlequin about them, but the heating coil wasn't that big and you lost quite a bit of cylinder volume with that and the DHW coil. So moved to UVC, which is a good solution, either big coil, or existing cylinder with PHE and pump.

[dpmiller]

25 minutes ago, Iceverge said:

@dpmiller

 

Did you install the Harlequin Heatstream in the end? 

 

I really liked the idea but thought the storage volume too small. If they could make an really big one it would be ideal for an ASHP. 

Nope, they pulled the more complex versions from sale. I looked at the Copperindustries MaxiPod, but ended up getting Worldheat to make me a TS with similar characterisitics- manual fill, big coils, direct connections for a stove.

[Iceverge]

Nice, what size did you go for? 

 

What would you estimate the temperature of the TS when it can no longer provide DHW ? 

[Iceverge]

3 hours ago, JohnMo said:

Big Red heat pumps used to do them. Spoke to Harlequin about them, but the heating coil wasn't that big and you lost quite a bit of cylinder volume with that and the DHW coil. So moved to UVC, which is a good solution, either big coil, or existing cylinder with PHE and pump.

 

The Harlequin I liked because it was square, plastic (no corrosion) and had all the connections on top. However 210l was far too small in my opinion without a gas or oil boiler on call. Also it couldn't be plumbed to a solid fuel loop. 

 

I can see the attraction of a PHE type too. 

 

What about one of the Gledhill Torrent Heat banks and an ASHP. It might work as an off the shelf solution. 

 

Of course the obvious answer of course is an UVC but the G3 servicing can add up over time. 

 

 

[dpmiller]

1 hour ago, Iceverge said:

Nice, what size did you give for? 

 

What would you estimate the temperature of the TS when it can no longer provide DHW ? 

 

It's about 270l full, a 300 shell with expansion volume; and both the ASHP and DHW coils are around the 3m2 mark. I run the DHW from the heat pump at a 51c setpoint and a 2c hysteresis, so what with stratification and deltaT on the flow the top of the tank is 55-57c. The sensor is halfway down, between the DHW and ASHP coils. Myself or Boy Wonder can have a shower before the heatpump cuts in, better half about 3/4 of a shower. But the output temp never drops noticeably as the heatpump is quick enough to replenish the heat...

So at reasonable flow rates I only see a few degrees between TS temp and DHW at the tap.

Also, in the cold weather I run a timed boost on the upper immersion at getting-up time so the heatpump can focus on charging the slab without unneccesary defrosts. At E7 rates I'm sure the difference in COP makes minimal difference.

Obviously if the stove is/was lit, or the sun's been out and the diverter has been busy, there's a lot more energy to play with too.

[Jane W]

The only thing that seems very clear to me atm is that there are SO many possible options. Having learnt a great deal by reading various threads, but not enough yet to make a good well-informed decision I'm still considering gas but with a system boiler and UVC. Use the solar pv to feed into heating dhw or maybe solar thermal as an alternative to pv. In the Denby Dale House they prevented some of the cycling by diversion to heat incoming air supply in mvhr. I'm not exactly sure how that works but I like that idea. I may also need ac cassette to pass part O and of course this could be used to heat as well, as suggested on here somewhere. If I'm not careful I'll have an unaffordable selection of heating methods that may not be needed very much because of (hopefully) a fairly low heating demand. Some of the total heating and hot water mvhr solutions also seem pretty good and I haven't yet discounted the idea of an ashp🤷‍♂️

[Iceverge]

Sorry, I've just skimmed the thread again and I didn't see any reference to your heating requirement in kW or your lightly usage of DHW/occupancy. 

 

How well insulated and airtight is the house? Do you have. Triple glazing or MVHR? 

 

 

[Jane W]

8 minutes ago, Iceverge said:

Sorry, I've just skimmed the thread again and I didn't see any reference to your heating requirement in kW or your lightly usage of DHW/occupancy. 

 

How well insulated and airtight is the house? Do you have. Triple glazing or MVHR? 

 

 

It hasn't been calculated yet as I'm at the very beginning of the process but really want to get the options considered so it's not a rushed decision. Looking at full fill cavity, 150mm on short sides (north and south) and 200mm on long sides east and west facing. Floor and roof as close to 0.1 as possible but dormers might compromise this. Would like triple glazing but costs seem so much higher than high performance double so probably end up with double. Going for good level of airtightness but style details like 1.5 storey with dormers might make this tricky in places. Taking inspiration as far as possible from Denby Dale case study but I understand that having dormers and 1.5 storey detailing will likely compromise overall airtightness. We're really keen to include mvhr.

[Jane W]

On 17/03/2024 at 11:52, JohnMo said:

 

Because they have an excellent turndown ratio. By that I mean minimum output which is something like 1.8kW, compared to must which have nearer 6kW for the same boiler rated max output. This helps minimise short cycling which can use lots of gas.

 

 

1.8kW is very low minimum output, that's so much better than I expected. 

[Jane W]

On 17/03/2024 at 12:37, Iceverge said:

Interesting topic this one. 

 

I laboured over the best DHW solution for ages. Ended up at a direct 300l UVC, mostly because I was sick of all the sales nonsense and high capital outlay. It works fine and doesn't cost too much to heat. Hopefully very little whenever I put in some PV. 

 

On my plumbing research travels I became quite attached to the idea of Thermal stores. I subsequent installed a 250l maxipod thermal store in my parents house to merge an oil boiler and a solid fuel Rayburn to deliver pressurised hot water. It works really excellently. Instant hot water, no G3 or discharge pipework to worry about. 

 

However It needs to be kept at a high temperature to deliver any reasonable amount of DHW. Not ideal for an ASHP. 

 

You could just get a massive coil in tank TS (say 600l) and it'd work fine I bet. 

 

 

I've read little about thermal stores so far...is it really just a larger cylinder?

[JohnMo]

7 hours ago, Jane W said:

I've read little about thermal stores so far...is it really just a larger cylinder?

It's basically a cylinder full of heating water, not drinking water, it uses a coil or plate heat exchanger to make hot water for the taps. An unvented cylinder is the other way about. A cylinder full of drinking quality water heated by a coil or heat exchanger. An unvented cylinder is serviced annually because it's a pressure vessel, the thermal store is open vented so does not have the same legal requirement.

 

However for the same size of cylinder an unvented cylinder delivers way more usable water. I had a thermal store and changed to unvented, it's way better.

 

Regardless of heat source, gas or heat pump always install a heat pump cylinder with a 3m2 coil. For gas you can run in condensing mode and have quick recovery times. 

 

Once you are well insulated you create problems for heating control if you try to over think it, you need to keep things simple and the heating system open.  UFH works well, with a thick screed, it becomes a storage heater, ideal for cheap electric tariffs and ASHP or blasting heat in once (35 deg flow for about 3 to 8 hrs) a day from gas.

 

At it's simplest you need a good gas boiler (Atag, Intergas, Viessmann) or heat pump, a cylinder and 3 port diverter valve, UFH manifold (no pump mixer or actuator). The manufacturer controller or a single thermostat. Run a boiler on Priority hot water or W or X plan (nothing else). This will give two output temperature from the boiler one for heating the other for hot water. Cheap boilers don't do this. ASHP do this by default.

 

We went from gas to ASHP mostly to get cooling.

[JamesPa]

On 17/03/2024 at 13:37, Iceverge said:

Interesting topic this one. 

 

I laboured over the best DHW solution for ages. Ended up at a direct 300l UVC, mostly because I was sick of all the sales nonsense and high capital outlay. It works fine and doesn't cost too much to heat. Hopefully very little whenever I put in some PV. 

 

On my plumbing research travels I became quite attached to the idea of Thermal stores. I subsequent installed a 250l maxipod thermal store in my parents house to merge an oil boiler and a solid fuel Rayburn to deliver pressurised hot water. It works really excellently. Instant hot water, no G3 or discharge pipework to worry about. 

 

 

 

I've said it many times, but I am convinced there must be a better solution to ensure the safety of a uvc than the current one, particularly when used with an ashp which is incapable of boiling the water.  The discharge pipework is a major hurdle for retrofit situations.  If we dispense with it then fitting a uvc is a no brainer.  If only the industry could be persuaded to think outside the box on this one!

 

In an ashp system, if we dispense with the in-cylinder immersion, (use a Willis heater located elsewhere as a backup) then any number of safety features could be added to ensure water reaching the DHW heating coil never goes above say 75C.  What's the actual residual risk if we do this?

 

I know someone will quote the D1,D2, tundish... guidance (the actual mandatory regs don't mandate a solution, only a requirement that it is safe), but the problem is significant enough to justify rewriting the guidance if there is an alternative safe solution.

Edited May 2 by JamesPa

[JohnMo]

1 hour ago, JamesPa said:

I am convinced there must be a better solution to ensure the safety of a uvc than the current one, particularly when used with an ashp which is incapable of boiling the water.  The discharge pipework is a major hurdle for retrofit situations

The alternative has always existed Vented or thermal store, such as a Harlequin - no discharge piping, no G3. Fit for purpose, vented is what most old houses have anyway.

 

1 hour ago, JamesPa said:

use a Willis heater located elsewhere as a backup) then any number of safety features could be added to ensure water reaching the DHW heating coil never goes above say 75C

Same as an immersion in cylinder just moved so it doesn't sound as bad - same effect on UVC if it goes wrong.

 

You keep trying to reinvent a wheel which is never going to happen. If don't want G3, use a different technology that doesn't need it.

 

Edited May 2 by JohnMo

[MikeSharp01]

Surely the tundish can just vent into an internal drain or is an outside vent obligatory?

[JohnMo]

6 minutes ago, MikeSharp01 said:

Surely the tundish can just vent into an internal drain or is an outside vent obligatory?

Internal drain is fine

[joe90]

6 minutes ago, JohnMo said:

Internal drain is fine

I was told by my plumber who signed off my tank not, it must be visible to be “venting”, was he wrong?

[JamesPa]

35 minutes ago, JohnMo said:

You keep trying to reinvent a wheel which is never going to happen.

All I am trying to do is solve a real problem.  What's wrong with that?  

 

And why is it never going to happen.  No laws of physics are violated so is it 'never going to happen' because the industry either doesn't want it to or can't think out of the box?  

 

I'm not sure why it's necessary to be so dismissive, there is a problem to solve, let's try at least to postulate a solution.

 

Obviously for new build there is no problem, but we have 1.4M gas boilers in existing buildings to replace with ASHPs each year for probably 20 years, and uvc minus the difficult discharge requirements would make a good proportion a lot easier and a lot cheaper.

Edited May 2 by JamesPa

[JamesPa]

1 hour ago, JohnMo said:

2 hours ago, JamesPa said:

use a Willis heater located elsewhere as a backup) then any number of safety features could be added to ensure water reaching the DHW heating coil never goes above say 75C

Same as an immersion in cylinder just moved so it doesn't sound as bad - same effect on UVC if it goes wrong.

Not necessarily.  By separating it from the tank you have the option, in a fault scenario, to dump or divert the hot water it produces before it even reaches the tank.

[MrPotts]

12 hours ago, Jane W said:

It hasn't been calculated yet as I'm at the very beginning of the process but really want to get the options considered so it's not a rushed decision. Looking at full fill cavity, 150mm on short sides (north and south) and 200mm on long sides east and west facing. Floor and roof as close to 0.1 as possible but dormers might compromise this. Would like triple glazing but costs seem so much higher than high performance double so probably end up with double. Going for good level of airtightness but style details like 1.5 storey with dormers might make this tricky in places. Taking inspiration as far as possible from Denby Dale case study but I understand that having dormers and 1.5 storey detailing will likely compromise overall airtightness. We're really keen to include mvhr.

From what I have read the additional cost doesn’t justify triple glazing over double glazing.

[sharpener]

57 minutes ago, joe90 said:

I was told by my plumber who signed off my tank not, it must be visible to be “venting”, was he wrong?

 

AFAIK it has to be "visible" somewhere, Ariston MIs say ideally at both locations but if "practically difficult" one is sufficient so just at the tundish will do, mine is in the airing cupboard. D2 goes into a waterless trap on the soil stack. Was signed off by the plumbers who did it.

 

Have moved the trap lower down so there is more head but on test at full flow I can still hear it backing up to the tundish, D2  complies with the rules, have stopped worrying.

[Iceverge]

12 hours ago, Jane W said:

It hasn't been calculated yet as I'm at the very beginning of the process but really want to get the options considered so it's not a rushed decision. Looking at full fill cavity, 150mm on short sides (north and south) and 200mm on long sides east and west facing. Floor and roof as close to 0.1 as possible but dormers might compromise this. Would like triple glazing but costs seem so much higher than high performance double so probably end up with double. Going for good level of airtightness but style details like 1.5 storey with dormers might make this tricky in places. Taking inspiration as far as possible from Denby Dale case study but I understand that having dormers and 1.5 storey detailing will likely compromise overall airtightness. We're really keen to include mvhr.

 

The best bang for your buck in terms of energy saving + comfort is.

 

1. Airtighness 

2. MVHR

3. Triple glazing 

 

Have you considered higher quality uPVC 3g windows. Something like Veka 82 or Kommerling 88 or Gealan S7000.  They're both the cheaper and better performing than almost any aluminium or timber window. 

 

I'm going to pull a figure out of thin air here of a heating demand of 40kWh/m²/annum and a peak heating load of 20W/m². Say you're 200m² then that's 4kW. A 5 to 8kW heat pump would work well. 

 

My recommendation is a monoblock ASHP with single zone UFH on the ground floor only in 1 zone and a 300l UVC. Electric UFH just under the tiles in all bathrooms including those already with wet UFH. Maybe @Nickfromwales can disagree. 

 

 

 

 

 

 

 

[JamesPa]

2 minutes ago, sharpener said:

 

AFAIK it has to be "visible" somewhere, Ariston MIs say ideally at both locations but if "practically difficult" one is sufficient so just at the tundish will do, mine is in the airing cupboard. D2 goes into a waterless trap on the soil stack. Was signed off by the plumbers who did it.

 

Have moved the trap lower down so there is more head but on test at full flow I can still hear it backing up to the tundish, D2  complies with the rules, have stopped worrying.

That must be ok because draining to a suitable internal soil stack is a recognised solution.

[Iceverge]

5 minutes ago, MrPotts said:

From what I have read the additional cost doesn’t justify triple glazing over double glazing.

 

What about thermal comfort and noise.