Quote:
Originally Posted by jeff5may
I have more HDD's than CDD's on paper, but the summer climate has lots of latent energy in it. It tends to be muggy and swampy here a lot. Even during heating season.
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That is really an excellent point. You have correctly identified a deficiency in the terms HDD and CDD. The idea of HDD and CDD is to have a statistical, localized value to use as an aid in designing heating and cooling systems, but both HDD and CDD ignore the part that humidity plays in the design. You are right, the humidity plays a very large part. I would assume that local designers would learn from experience, and develop a 'fudge factor' to make localized corrections. But it does seem inelegant.
A few years back, I was trying to zero in on exactly what my heating requirements actually were. I was doing a study in which I was heating my house with several electric resistance heaters, and I had a Kill-a-Watt attached to each. I was logging outdoor temperatures during this time, and plotting temperature against power, expecting to get a fairly smooth curve that I could then use to precisely model heating needs of my house. I was amazed at the scattering of data points I was getting, and what I thought would be some kind of a curve, was actually a cloud of points. What you have identified, explains the scattering, because I had not accounted for variations in humidity, and the power that would be required to deal with that humidity.
But back to the HDD & CDD issue, this is a very good reason to do a concept 'upgrade' of Heating Degree Days to Heating BTU Days, HBD (with the metric equivalent being Heating Kw-h Days, or HKD) and instead of Cooling Degree Days, they would become Cooling BTU Days, CBD (ditto metric equivalent, Cooling Kw-h Days, or CKD). This would incorporate average humidity for various months.
It's an important distinction.
jeff5may, I think we should prepare to storm the halls of science...
-AC