"Terry" wrote in message
. ..
Nick wrote?

Moving a pound of 55 F 100% RH basement air with 0.0093 pounds of
water vapor up into an airtight house and warming it to 65 with
0.24(65-55) = 2.4 Btu and drying it to 30% RH so it contains 0.004
pounds of water, releasing 1000x5.3 = 5.3 Btu, provides 5.3-2.4 = 2.9
Btu more heat than the electrical energy needed to operate the
dehumidifier.

can you run that past us again please?
Namely;
One pound of air containing 0.0093 pounds of water raised by (65-55= 10
deg. F) = 0.093 BTU?
Drying (removing) out the water from 100 to 30 per cent = 0.0093 * 0.7 =
0.0065 lbs.
Heat released from that 0.0065 lbs of water would be .....................
??????
And that's the point where I lost it!
Can you help me out?

What Nick was saying, is one pound of 55F air at 100% RH contains 0.0093
pounds of water. After you heat it up and dry it down to 30% RH, it has
0.004 pounds of water, so you've removed 0.0053 pounds of water as
condensate.

Nick then approximated the amount of heat given off by 1 lbm of water when
it is condensed as 1000 BTU (its a little more, but that's a nice round
figure). So if 1 lbm of water vapor gives up 1000 BTU, then 1000 BTU/lbm *
0.0053 lbm = 5.3 BTU given up by the condensing of 0.0053 pounds of water
found in one pound of air.

It takes about 0.24 BTU to warm up one pound of air by one degree. So to
warm up the air from 55F to 65F would take about 0.24 BTU/lbm-F * (65-55) =
2.4 BTU for every pound of air.

So, starting with air at 55F at 100% RH (call it state 'A'), if you run it
through 'some process' to get to 65F at 30% RH and some condensate (state
'B'), you have to add 2.4 BTU sensible heat to warm each pound of air, and
the vapor releases 5.3 BTU/lbm of latent heat to condense the water vapor
from one pound of air, so you have a net excess of 2.9 BTU for each pound of
air you run through this 'process'.

But that doesn't tell you how much energy you have to expend to get each
pound of air from point 'A' to point 'B'.

daestrom