It seems not so good savings then? I went through it to check, I used 24 months data and 2011 months from 20deg C;
Description:,"Celsius-based heating degree days for a base temperature of 20.0C"
Source:,"www.degreedays.net (using temperature data from http://www.wunderground.com)"
Accuracy:,"Estimates were made to account for missing data: the ""% Estimated"" column shows how much each figure was affected (0% is best, 100% is worst)"
Station:,"Hobart Airport, AU (147.50E,42.83S)"
Station ID:,"YMHB"
Month starting,HDD,% Estimated
2010-05-01,294,0.1
2010-06-01,332,0
2010-07-01,346,0
2010-08-01,342,0
2010-09-01,295,0
2010-10-01,227,0
2010-11-01,188,0
2010-12-01,152,0.03
2011-01-01,94,0
2011-02-01,123,0
2011-03-01,163,0
2011-04-01,196,0
2011-05-01,295,0
2011-06-01,332,0
2011-07-01,368,0
2011-08-01,278,0
2011-09-01,270,0
2011-10-01,251,0
2011-11-01,153,0
2011-12-01,147,0
2012-01-01,106,0
2012-02-01,103,0
2012-03-01,146,0
2012-04-01,183,0
so the 7 months total to 1990 degree days
The discount factor (100%) you have applied to the gradually diminishing temperature period between 10pm and 6am is too severe I think, for sake of argument say average temperature in that period is 18 degrees, the heat is still flowing out for those 8 hours and that heat is required to be replaced at 6am when heater is on and starts to ramp up, hence I would use;
16*(5.9-3.408)*1990/1000=79.3
plus
8*(5.9-3.408)*1990*.8/1000=31.73 [.8 adjusts for lower average temperature]
sum is 111
I am vaguely recalling now how I came to my 'hoped for' figure. From my head I used something liked 9 degrees and 2.5 watts per square metre and 300 days, which gives around 162kwh. Historically we would use the heater on far more than 214 days for some time during the day.
In fact the situation is even less sound since the primary heat used is a heat pump with COP rated at 2.6. I suspect that the practical COP is less.
On the bright side, if lower thermal losses result in having the heater off for more hours, there is a heater overhead of 2-300 watts I think, which will be saved and that could add up.
It will be interesting to make an assessment in the light of these figures.
In any case if the real energy savings are as stated they will save 9*111/2.6=384kwh
@ 330g CO2 per Kwh, hence 126kg CO2 Tasmanian average emissions saved, or 384*1.1=422kg if incremental emissions are considered for use of Victorian brown coal through Basslink. ( we have typically been importing power in recent years, since the drought has lowered hydro storages)
Posted Tuesday 22 May 2012 @ 12:34:04 pm from IP
# 
