if i was building tomorrow and i could build the envelope i wanted i would use:
a HVAC system with heat recovery.
A small electricial element in the HVAC system would be my heat source, heatingthrough air ducts.. .no water space heating at all.
Domestic hot water would be by solar panels alone.
This is assuming 'passive' standard build.
If you have a passive house your system could be up to 90% efficient meaning over 24hrs the temp would drop from 20c to 18c. (figures just for example)
I find it hard to believe these figures. I am in favour of HRV but I believe achieving such figures are next to impossible WITHOUT use of significant energy - ie a heat pump - which most HRV systems incorporate.
I know you are not making up these figures, the HRV sales people spout them all the time. The only problem is that they are practically impossible to achieve - WITHOUT supplying significant energy to the system. Would love for someone to come along and prove me wrong.
Are you saying you doubt the whole passive house principle?
Incidently, most HRV system do no not incorporate a heat pump from my enquiries.
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This is the SAP report from a HRV I was considering using done by the BRE.
This does not have a heat pump.
This confirms heat recovery of around 90% with very little energy usage.
NO!!!! - On the contrary I think the passive house concept is terrific. But I do doubt the 90% efficent claims for HRV - in fact I believe it is more like 40-50% - which is still excellent. I just wish salesmen would tell it like it is. I would advise anyone building today to massively insulate, glazing to south, sheltered site etc etc ... AND use HRV but do not expect miracles from HRV. Use it as a simple ventilation system with some of your expelled air-heat recovered. And when I say some I mean a lot less than 90%.
Maybe I am not informed enough. But I see brochures that state things like....they use 20 watts - BUT they have a boost button which then consumes 250-350 watts - that, I guess, is the heat pump - what else can it be??? Maybe some form of electrical heating??
Is there a HRV expert here who can clarify? Where is the 300-350 watts going? It is not moving a fan - it must be either working a heat element or a heat pump.
You are going to have to forgive my ignorance here. What does "90% heat recovery" mean? For example:
If the internal air temp is 20 deg C and the outside is 0 deg C - what will the incoming air temp be after it has passed thru the heat exchange system?? Will it be 18 degrees? My bet is that it will be at the very best 10 degrees. But most likely 7-8 degrees.
Now please note that I am not knocking HRV - I think they are useful - just not as good as they are made out to be in terms of efficiency. But it seems impossible to me that you can recover 90% of the difference between the incoming and the outgoing air temperatures. Maybe my interpretation of 90% efficency is incorrect - but then I have met a lot of HRV salesmen.
As regards the efficiencies, my understanding is that it relates to the percentage of heat recovered from the stale air leaving the house i.e. 70% efficiency for 10 degree extract air means that the air actually vented to the outside will be 3 degrees, with 7 degrees having been recovered. That 7 degrees is transfered to the incoming air and has an effect on it but obviously that depends on the temperature of the incoming air. My physics isn't good enough to understand it fully but this is how I understand it in simple terms.
I have found this thread really interesting and wonder is anyone interested in doing something like this http://www.boards.ie/vbulletin/showt...p?t=2055263818 here. Syd put me on to it earlier in this thread.
I think if we could get together installation c and running cost of systems it would give people a better idea of the system to pick for their own home.
Anyone up for it?
I don't dispute the idea but I would wonder how many people on here actually have HRV?
That heatpump thread is different because everyone in the country that was building one offs fell for that craze over the last 5 years. Now the biggest Irish manufacturer of them has gone to the wall and no one will service the systems they put in. How long before lots of the little guys importing various heat pumps also disappear and leave people high and dry.
Of course this leads back to the question already raised about servicing and repair on HRV but I don't think it's quite the same issue as I've raised about heat pumps. The cost of a HRV system isn't massive (compared to say a heatpump) and they are not terribly complicated either I gather. Plus when kingspan start flogging something it certainly suggests that they are going mainstream, i.e. every plumber will know how to service them soon enough.
I also agree with the concept of keeping it simple but the issues are interlinked. Adding lots of insulation will only add benefit when a structure is airtight. If the structure is airtight all practicality suggests that HRV is the best way to ventilate.