need to learn heating/cooling calcs.
I am re-doing our house from the footing up, I intend to super-insulate with approx. r-19 foundation walls, R-60 walls, and ceilings, and energy recovery ventilation, with silicon weatherseals at all doors and windows, courtesy of Conservation Resourses. I’m wanting to do in-floor radiant heating with solar collectors for the hot water source, and a high efficiency a/c air handler for de-humidification. What resources do I study to learn the necessary heating/cooling load calcs. and where can I find the necessary parameters for sizing my ducts as I know the current layout sucks. Fouteen years of discomfort speaks loudly.
And from the current discussion on insulating with foam, I’m trying to decide if 9 inches of isocyanoacrylate in a SIP Panel is overkill, or just good conservative design. I’m keeping the existing windows, mostly, and adding properly sized over-hangs to reduce unwanted heat gain in the summer.
So, teach me Oh Masters.
P.S. I’m resorting to doing the calcs myself because I’ve contacted three different ‘reputable’ HVAC companys in the area and they all give me these oversized designs that are going to short cycle and not reduce the humidity at all.
Replies
"they all give me these oversized designs that are going to short cycle and not reduce the humidity at all."
I'd venture to guess that if you know this for a fact, then you already know how to do the calculations, right?
;)
Seems to me, that with R60, you shouldn't need any normal heating system. Run the pex in floor and pump from the domestic hot water heater, with a solar preheat storage.
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CLupis
Manual J is one place to start. Here is one place to get it, there are others.
http://www.hvaccomputer.com/gtarget1.asp?kwx=11&adx=10&gclid=CIWn6pX8v50CFQ_xDAodUWEziQ
Duct sizing start.
http://www.engineeringtoolbox.com/sizing-ducts-d_207.html
KK
Many thanks for the references. I'm great on theory but, way short on practicum. Ergo I need to be able to show the calcs to the plan reviewer for my permits.
HVAC calc does not allow you to be that exacting in defining the structure. It is fine for more standard construction. But not for this..
William the Geezer, the sequel to Billy the Kid - Shoe
Cutting to the chase, you're saying that you disagree with the contractor as to the size of the air conditioner you need. You believe your design will not need as much as they want to sell you.
I don't see what the problem is. Ask them to instal two small units, and set them up with the appropriate controls to either alternate between them, or run both at once when needed.
The basics of this are pretty straightforward; I would think you could use a standard sump-pump control panel for this. That is, hook up two thermostats in place of two of the floats, disconnect the alarm contact, and jumper the 'low' float contacts. (I say do this, because the thermostats have a built-in 'dead zone' to prevent short cycling). Then set one thermostat a bit higher than the other.
Likewise, the issue of the blower operation can be solved -at worst - by installing a second blower. I suspect that the units will let you get away with just one blower, though.
I think this arrangement will satisfy everyone.
Oh, a final thought: Look for an HVAC firn whose owner is also a PE.
Edited 10/16/2009 1:51 pm ET by renosteinke
I've used an age old reference I got in college ... "Concepts in thermal Comfort" by M. David Egan. Great simplified ASHRAE calcs that give you a step by step design load procedure. You could likely pick up a used copy cheap at Amazon. It also has duct sizing in it.
It uses an old version of ASHRAE design sizing, but I figure it is reasonably accurate and usable.
IMO 9" is overkill if you are using what is considered in the 'minimum' low-e coated glazing. Someone who is willing to go the extra mile in the wall should certainly consider going the extra mile in the windows .... e.g. using Heat Mirror glass. Low-e coated glass and trible glazing simply don't compare ... IMO. Glass may be only e.g. 10% of your wall area, but can contribute to say 60+% of heat loss/gain. Your 9" over 6" gains you tiny percentage additional efficiency while the glass can increase efficiency (not to mention comfort) in a much more significant way.
Often people say they are designing efficiently, but ignore glass orientation and summer sun protection at the same time. Design is about the whole house, not just High R walls and ceilings. It's about orientation, window area, solar protection, solar invitation, etc. With an existing house, this may mean looking for opportunities and making compromises, but not without the ability to fine tune.