U-values of solid walls
George Winkle| Posted inPassivHauson
I asked a GSHP installer how they could work out heat loss for each room without knowing the construction characteristics of the walls, roof and floors and received the following answer “our technical design team have worked out based on building regulations the required U-value’s for different properties be it a new build, renovation or boiler replacement in an existing house”
这是一个常识的情况没有我,can they do this with any degree of accuracy or am I right to be suspicious of the results their averages produce?
They have also told me categorically that using compact collectors or two levels of single pipe collector will cause permafrost. Comments please.
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The answer they gave is complete BS (but you probably already knew that, eh? :-) ).
"our technical design team have worked out based on building regulations the required U-value’s for different properties be it a new build, renovation or boiler replacement in an existing house"
Let's parse that a bit:
"...based on building regulations the required U-value’s for different properties..."
Probably means that for new house they design the HVAC on an assumption of code-min for all walls windows roofs, etc, in which case they only need the dimensions of the walls & windows etc to get there. But if you're building better than code you'll be guaranteed that they'll be oversizing the equipment.
"...renovation or boiler replacement in an existing house"
Probably means they assume code min on any new exterior walls and windows, and just take some WAG at the heat load in the the boiler replacement cast based on the size of the pre-existing boiler and maybe adjust that based on fuel use.
Designing something as expensive as a GSHP system based on that type of methodology is a lousy, unprofessional way to go. It's fine to make budgetary ball-park estimates that way and adjust it later when the real loads can be calculated. If they won't/can't do it right (or even if they can), hiring an energy nerd or engineer to run the real calculations will be worth it, and it gives you something to sanity-check proposals with.
1The discussion has moved on to a "technical adviser". He wants to know the construction of roofs, wall material etc. I've offered to provide al of the measurements they require and to answer any questions they have about the building. What they want now are detailed plans and elevations - in their dreams!
Even limited internet research shoots yawning chasms in their arguments. The truth is they do not have the expertise to design a system but rely on double glazing sales techniques to sell over-priced installations to trusting people who are at sea with the poor information provided at enormous public expense by the Energy Saving Trust.