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Old 10-20-14, 02:28 PM   #1
buffalobillpatrick
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Join Date: Mar 2014
Location: Florissant, Colorado
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Default HP COP vs NG boiler $ Balance point

I want my Heating System controller (Arduino) to be able to automatically switch between HP and NG boiler, based on $ calculations.

Code must calculate the HP COP vs. Natural Gas $ Balance Point.

Code will use near real-time $ inputs for NG & Electricity (pots adjusted monthly), to calculate the $ balance point, calculate HP COP real-time,
then select HP or NG boiler.

Coefficient of performance - Wikipedia, the free encyclopedia

COP = Q / W
where
Q is the heat supplied to the reservoir.
W is the work consumed by the heat pump.

note: W is in Kwh & must include pumps.

In USA units:
Q = BTU/h = F x DT x 500 x SH
where
F is Gallons/min
DT is Delta Temperature *F between Load Out & Load In
SH is Specific Heat, water = 1, propylene glycol 30% water mix = .935

NG Mcf = 1,000 ft3
Therm = 100,000 BTU = 29.3Kwh
$Therms = $Mcf / 10.25

My energy prices vary greatly.
Over the past several winters my average delivered NG $8.00/Mcf = $.78/Therm
& delivered Electricity rate about $.16 / Kwh


Easy to use online Heat Cost calculator:
Electric Heat vs. Gas/Oil Heat Cost Calculator/Comparator

My Cost of heat (per 100,000 BTU)
$.16 / Kwh Electricity = $4.69
$.78 / Therm with 85% Efficiency NG boiler = $0.92

Convert to Balance point: 4.69 / .92 = 5.0978 COP

Balance Point Formula:
BP = ( $ per Kwh / (( $ per Mcf / 10.25) x (1 / Boiler Efficiency %))) x 29.3

COP of about 5.1 seems too high????

Please feel free to give corrections.............


Last edited by buffalobillpatrick; 10-20-14 at 03:31 PM..
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