Is this hot water system possible?

[Inchy]

Hi folks -

I'm about to start building a 3 storey 320m2 house with good levels of insulation, etc. As we're not on mains gas, I've been looking into possibilities such as heat pumps, solar etc, to provide central heating and hot water.

I've been looking at a product - Combi 185 - from a company called Genvex, which seems to cover all the bases for my build: it ventilates the house using heat recovery, provides the heating via ceiling ducts from the recovered heat, and also heats the hot water for baths etc from recovered heat too [although I don't think it can do central heating and hot water heating at the same time]. We're also fitting a woodburner, possibly with a backburner, and the Combi 185 can accept heat from the woodburner too to aid water heating.

The guy from the Genvex supplier seems to think it will be fine in my proposed house, but my concern is that the unit only comes with a 185L tank. Our house is going to have 2 baths, 3 showers and 5 sinks in total and I'm worried that the tank won't hold enough hot water for our needs [2 adults, 3 young kids but we intend to stay here for years so they'll soon be 3 adults!].

What I'm wondering is whether it's possible for the water from the 185L tank to be diverted from the unit into a bigger cylinder - say 300L - so that we would have 300L to draw on rather than 185?

Any ideas, or thoughts on alternatives? Should I go for electric showers for example, and let the 185L tank cover just the baths and sinks??

 

[Dan Robinson]

so they'll soon be 3 adults!].

hmmm I couldn't wait to leave home. That 's a big assumption .



This all sounds lovely, but have you actually lived iwth a wood burner long term? It's not all sugar and pie. This renewable energy malarky is great but not a good idea to rely on just yet. You are lucky in that you are doing a new build so can incorporate a lot into the design. Solar for hot water (50% annual needs at best). Ground source (although 3rd Rock Energy have got me VERY interested in air source) heating for both hot water and central heating. I would probably augment this with some for of Electric, LPG, Oil.

A lot depends on your ideas for backups. The advantage of Log burners is that they are simple, and logs are plentiful although they need to be dry; and its not the most reactive of heat sources.


Please don't see this as negative, I am all for saving the wallet, sorry PLANET. Luckily in todays economic environment it is easier to rectify the two. DO NOT be taken in by sales bumph. Remember the phrase Snake Oil .

Just this Saturday I went to a house that had had at least three people try and flog them Solar. Not one looked at the house aspect, storage areas, long term requirments or the simple logistics of installation. Ignoring for the moment that the panel would need mounting on an A-frame against the gable end of the house overlooking next door's back garden.

 

[JohnD]

Firewood is nice to use if you're fond of spiders and beetles running about the house.

 

[Paul Barker]

I would go for a seeperate solar hot water system to combine with the genvex and the log burner. I would expect that during the summer the solar is the cheapest hot water provider of the two as I would expect it to use less electricity to provide your hot water.

During the winter when the log burner is blasting away you and there is so much cloud cover insufficient uv rays approach your panel, the balance should tip to the heat pump some of the time anyway.

In the very long run heat pumps have to hope for the availability of cheap, and green (if we are genuinly interested in the planet and not our pockets and planning permissions) electricity. On my energy efficiency training I was defo told that electricity is a very dirty fuel, not green at all. Neither is it cheap. How long will the heat pump last? Quite some considerations.

When you use solar and heat pump for dhw I suggest you have a system seperate storage, so call for heat pump hot water only when solar is not available. Such a system is already on the market but you could reinvent the wheel your own way.

As for electric showers. TISH! That is a crazy cop out for someone genuinly green.

 

[Paul Barker]

Also consider: check with the heat pump company if the unit can be supplied with greater capacity or can be combined with adjacent unvented cylinder water circulated between the two with a pump.