How would you configure your new DHW and CH system?

[Pseusmyd]

I have been browsing this forum for a while and I would like to thank you all for the excellent posts which contain a wealth of information. Please keep going as they are very useful.

 

Currently, I am at the start of refurbishing a bungalow to a 5 bedroom house (280m2) which gives me the perfect opportunity to review my heating and energy saving requirements.

 

During this large refurbishment, I will be installing a MVHR system (Zehnder Q600) and a 5.5KW solar array. Downstairs will be wet UFH for about 70% over a newly installed slab, the rest 30% will be radiators over the suspended floors. Upstairs will be 100% radiators.

 

To configure how I would like my CH and DHW, I invited a couple of heating engineers to discuss my requirements. The following suggestions were giving;

 

1.       System boiler with one large unvented tank for UFH, radiators and DHW. Use of an immersun / iBoost.

2.       System boiler with one large unvented tank for UFH, radiators and DHW. Use of an immersun / iBoost and ASHP.

3.       Using the existing 38KW combi boiler for DHW. Install a system boiler with an unvented tank with an immersun / iBoost for UFH, radiators and an ASHP.

 

An ASHP has not been budgeted-in for the moment. Would installing 2x28mm to the outside be a good option for later? Would I need low temperature radiators for now? Will it work for later as the ASHP runs at a lower temp?

 

So, if you had to start from scratch, how would you configure your system?

[MikeGrahamT21]

What sort of insulation levels and airtightness are you expecting to achieve? Thats probably the main deciding factor for this.

[jack]

Welcome!

 

12 hours ago, Pseusmyd said:

1.       System boiler with one large unvented tank for UFH, radiators and DHW. Use of an immersun / iBoost.

2.       System boiler with one large unvented tank for UFH, radiators and DHW. Use of an immersun / iBoost and ASHP.

3.       Using the existing 38KW combi boiler for DHW. Install a system boiler with an unvented tank with an immersun / iBoost for UFH, radiators and an ASHP.

 

I find it interesting that all three recommendations include unvented tanks. I'd have thought they were the exception rather than the rule in modern systems, unless you need a massive tank to handle, eg, the output from a wood-fired boiler.

 

Definitely agree that knowing your energy requirements will be useful to give suggestions.

Was there a reason why you went for such a significant refurb rather than a knockdown and rebuild? Even without taking the VAT reclaim into account, the extend-and-refurb approach never looked good for us when planning to replace a ~90m2 bunagalow with a ~290m2 house, especially given the compromises it would have involved.

[Jeremy Harris]

24 minutes ago, jack said:

I find it interesting that all three recommendations include unvented tanks. I'd have thought they were the exception rather than the rule in modern systems, unless you need a massive tank to handle, eg, the output from a wood-fired boiler.

 

 

I've a feeling that there may be a bit of confusion between unvented (i.e. sealed and pressurised) hot water cylinders and vented (i.e. hot water cylinders with an open vent to a cold water tank).

 

Unvented cylinders seem to be the most popular now, I believe, probably because they give mains pressure hot water.

[jack]

8 minutes ago, Jeremy Harris said:

I've a feeling that there may be a bit of confusion between unvented (i.e. sealed and pressurised) hot water cylinders and vented (i.e. hot water cylinders with an open vent to a cold water tank).

 

Unvented cylinders seem to be the most popular now, I believe, probably because they give mains pressure hot water.

 

For some reason I read all three as "vented" - ignore me and carry on!

[PeterW]

Most of those I think if he is thinking of running a boiler and UFH and Rad circuit then I would be using a Thermal Store if your water pressure is good. 
 

 

[Pseusmyd]

On 27/04/2020 at 08:48, MikeGrahamT21 said:

What sort of insulation levels and airtightness are you expecting to achieve? Thats probably the main deciding factor for this.

Thank you all for the replies. The property will be well insulated, well above building regs standards as stated in the specification document designed by my architect. I am currently on furlough and foaming every crack and hole I can find before the insulated plasterboard gets installed by my contractor.

On 27/04/2020 at 10:44, jack said:

Was there a reason why you went for such a significant refurb rather than a knockdown and rebuild? Even without taking the VAT reclaim into account, the extend-and-refurb approach never looked good for us when planning to replace a ~90m2 bunagalow with a ~290m2 house, especially given the compromises it would have involved.

Very good questions, the honest answers is.....if I would do it again, it will be a knock down and rebuild. Currently the refurb will be cheaper but I agree, compromises had too be made. 

On 27/04/2020 at 11:06, PeterW said:

Most of those I think if he is thinking of running a boiler and UFH and Rad circuit then I would be using a Thermal Store if your water pressure is good. 

Water pressure is very good on site.

 

[MikeGrahamT21]

Might be a good idea for you to model your heat insulation levels using this tool: https://www.ubakus.de/u-wert-rechner/?

 

This will give you a good idea of the rate of heat loss, which in turn will inform your heating choice.

[Pseusmyd]

On 29/04/2020 at 08:37, MikeGrahamT21 said:

Might be a good idea for you to model your heat insulation levels using this tool: https://www.ubakus.de/u-wert-rechner/?

 

This will give you a good idea of the rate of heat loss, which in turn will inform your heating choice.

Thank you, 

 

It looks complicated but I will give it a try.

[MikeGrahamT21]

On 02/05/2020 at 15:49, Pseusmyd said:

Thank you, 

 

It looks complicated but I will give it a try.

 

Happy to do it for you if you let me know your final wall make up, type of materials and measurements.