Hybrid Car – More Fun with Less Gas

Night ventilation

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Posted by Nick Pine on November 15, 2006, 10:43 am
 
This simulation of automatic night ventilation over an average July day
in Rochester NY with 4 ft^2 of vent area at the top and bottom of a small
2-story house with 1200 pounds of water in 4" PVC pipes under a shiny
ceiling to store overnight winter heat from a sunspace shows the house
can be comfortable with no AC and 20 kWh/day of internal heat gain from
electrical use or unshaded windows, with about 600 cfm of natural airflow
for about 14 hours per day, when it's cooler outdoors. Doubling the vent
area lowers the max indoor temp about 1 F. Doubling thermal mass drops it
4 F. The mass stays well above the average 61 F dewpoint.

There will be a 1000 gallon heat storage tank in the basement for 5 cloudy
days and hot water for showers, heated with 64' of fin-tube pipe in an air
heater inside a sunspace, but we want to keep that hot for DHW in summertime.
As an alternative, one of two stratified tanks in the basement might be cool
in summertime.

20 PI=4*ATN(1)
30 W=2*PI/24'angular freq (radians)
40 C200'house thermal mass (Btu/F)
50 G0'house conductance to outdoors (Btu/h-F)
60 AV=4'vent area (ft^2)
70 HV'vent height difference (feet)
80 ECON`0'internal electrical use (kWh/month)
90 DGAIN412*ECON/30'internal heat gain (Btu/day)
100 HGAIN=DGAIN/24'internal heat gain (Btu/h)
110 TRp.2'average July temp in Rochester NY (F)
120 FOR D= 1 TO 10'simulate for 10 average days
130 FOR H=0 TO 23
140 Tp.2+(80.7-70.2)*SIN(W*H)'outdoor temp (F)
150 Q=HGAIN+(T-TR)*G'heatflow from walls into room (Btu)
160 IF T>TR THEN CFM=0:GOTO 190'no venting
170 CFM.6*AV*SQR(HV*(TR-T))'vent airflow (cfm)
180 Q=Q-CFM*(TR-T)'lower heat gain by venting
190 TR=TR+Q/C'new house temp (F)
200 IF D AND H MOD 2 = 0 THEN PRINT T,TR,CFM
210 NEXT H
220 NEXT D

hour   outdoors           indoors       cfm

0      70.2 (F)           68.5808 (F)   0
2      75.45              70.7387       0
4      79.29327           73.0518       0
6      80.7               75.34551      0
8      79.29326           77.41766      0
10     75.45              78.69283      449.4819
12     70.2               76.91831      751.8333
14     64.94999           72.89406      843.9746
16     61.10673           68.78081      823.9965
18     59.7               66.10492      727.5638
20     61.10674           65.48225      558.7523
22     64.95001           66.67577      258.8256

When I disabled venting by commenting out line 180 above,
the house got very uncomfortable:

0      70.2               92.42486
2      75.45              92.82798
4      79.29327           93.51543
6      80.7               94.30314
8      79.29326           94.98013
10     75.45              95.36509
12     70.2               95.35495
14     64.94999           94.9525
16     61.10673           94.26566
18     59.7               93.47852
20     61.10674           92.80206
22     64.95001           92.41759

So we might have a 2'x2' vent with a one-way plastic film damper near
the floor that lets cool air flow into the house, with a plywood door
or a 2-watt motorized foamboard damper over that which can be closed
if the house becomes too cool, eg less than 65 F.

Nick


Posted by George Ghio on November 15, 2006, 10:50 pm
 
Very impressive. But have you done it? You talk the talk, do you walk
the walk.

This sounds like a weather forecast. Not a great recommendation.

Why don't you build it, then you can show us your theory and the reality
side by side.

I can tell you that it will work but will not match your prediction.

Nick Pine wrote:

Posted via a free Usenet account from http://www.teranews.com


Posted by Solar Flare on November 16, 2006, 2:23 am
 We had houses like that but the occupants all died from cooking carbon
monoxide build up.



Posted by Abby Normal on November 16, 2006, 12:26 pm
 
Solar Flare wrote:

Lol never argue with Nick when he is deriving PI


Posted by Solar Flare on November 16, 2006, 11:08 pm
 I wasn't



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