Nathan and I have settled on a mini-pc for a smart whole house fan controller
that turns off an AC and runs a fan when it's cooler outdoors, and turns off
a heater and runs the fan when it's warmer outdoors and the air is dry enough
so there's no chance of condensation:
TU System 128mb ram + 512mb flash + Desktop Linux = $115 from
It uses 15 watts. Is there a way to reduce the power, and does it
have 256 or 512M flash memory? It also comes with a wireless option.
We found Atmel BASIC constraining, altho your displays seem nice.
Does it have a Roman numeral arithmetic package? My first programming
language did, with error messages like "wrong Roman constant."
We are planning to use 2 $44 TAI 8540A 1-wire RH & temp sensors from
and a $27 DS9490R 1-wire adapter, with OWFS as a 1-wire driver, and an X10
interface, eg the $69 2414u from http://www.smarthome.com/2414u.html or
Home Depot (are these too smart to program via linux?) with X10 controllers
for an AC, a heater, 2 fans and a damper, eg $11 15 amp AM466s from
http://www.hobby-boards.com/catalog/index.php?cPath $ has more fun stuff.
We are also looking at bwbasic, which appears to be about as old as gwbasic.
Here's an ASHRAE 55-2004 comfort calc done both ways:
50 CLO = 1'clothing insulation (clo)
60 MET=1.1'metabolic rate (met)
70 WME=0'external work (met)
80 TA.6'air temp (C)
90 TR.6'mean radiant temp (C)
100 VEL=.1'air velocity
120 RH†'relative humidity (%)
130 PA=0'water vapor pressure
140 DEF FNPS(T)=EXP(16.6536-4030.183/(TA+235))'sat vapor pressure, kPa
150 IF PA=0 THEN PA=RH*10*FNPS(TA)'water vapor pressure, Pa
160 ICL=.155*CLO'clothing resistance (m^2K/W)
170 M=MET*58.15'metabolic rate (W/m^2)
180 W=WME*58.15'external work in (W/m^2)
190 MW=M-W'internal heat production
200 IF ICL<.078 THEN FCL=1+1.29*ICL ELSE FCL=1.05+.645*ICL'clothing factor
210 HCF.1*SQR(VEL)'forced convection conductance
220 TAA=TA+273'air temp (K)
230 TRA=TR+273'mean radiant temp (K)
250 TCLA=TAA+(35.5-TA)/(3.5*(6.45*ICL+.1))'est clothing temp
260 P1=ICL*FCL:P2=P1*3.96:P3=P1*100:P4=P1*TAA'intermediate values
330 N=0'number of iterations
340 EPS=.00015'stop iteration when met
350 XF=(XF+XN)/2'natural convection conductance
370 IF HCF>HCN THEN HC=HCF ELSE HC=HCN
400 IF N>150 GOTO 550
410 IF ABS(XN-XF)>EPS GOTO 350
420 TCL0*XN-273'clothing surface temp (C)
440 HL1=.00305*(5733-6.99*MW-PA)'heat loss diff through skin
450 IF MW>58.15 THEN HL2=.42*(MW-58.15) ELSE HL2=0'heat loss by sweating
460 HL3=.000017*M*(5867-PA)'latent respiration heat loss
470 HL4=.0014*M*(34-TA)'dry respiration heat loss
480 HL5=3.96*FCL*(XN^4-(TRA/100)^4)'heat loss by radiation
490 HL6üL*HC*(TCL-TA)'heat loss by convection
510 TS=.303*EXP(-.036*M)+.028'thermal sensation transfer coefficient
520 PMV=TS*(MW-HL1-HL2-HL3-HL4-HL5-HL6)'predicted mean vote
530 PPD0-95*EXP(-.03353*PMV^4-.2179*PMV^2)'predicted % dissatisfied
540 GOTO 580
580 PRINT TA,RH,CLO,PMV,PPD
19.6 86 1 -.4778556 9.769089
After removing the comments with something like
sed "s/'.*//;" gwfile.bas > bwfile.bas
and adding back 'THEN's which bw complained were out of spec, eg in
410 IF ABS(XN-XF)>EPS GOTO 350
19.6 86 1 -0.4778564 9.7691115
which seems close enough :-)
Have you considered one of the gumstix computers? They may not be any
cheaper but the base configuration gives you a couple of serial ports
and only uses about half a watt, less when idle. They can run Linux
and use CF memory.
Then again, how fast a computer do you need for this kind of stuff?
Have you considered a PDA? They come with their own display and are
pretty thrifty with the power requirements.
For that matter, you might even go so far back as the famous Radio
Shack Model 100 which crops up on Ebay for $20 or so pretty regular.
It only uses a watt or so and has basic built in. :)
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