Appendix G
Thermostat Staging Algorithm
·Unit Default: Algorithm is initiated with Low Heat for 16 minutes. If call for heat still exists, unit transfers into High Heat until thermostat is satisfied.
·Low Heat run time is calculated based on previous heating cycle.
·High Heat on time is not calculated. High Heat is energized 1 of 3 ways and runs until thermostat has been satisfied.
1.After Low Heat has run for 16 minutes and call for heat is still present.
2.When algorithm does its calculation of previous cycle and determines High Heat is necessary.
3.After the amount of calculated Low Heat on time has elapsed and there is still a call for heat present.
·The following flowchart shows how the algorithm calculates low heat on times. To use calculations, the amount of time unit ran in Low Heat (LH) and High Heat (HH) during previous cycle must be known. The algorithm uses these values to decide which stage of heat should be initiated on next call for heat.
·Four examples also follow illustrating what the unit will do on a cold start, coming out of night setback, coming on in low fire, and coming on in high fire.
EXAMPLE 1: |
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Furnace ran for 16 minutes in Low Heat and 5 minutes in High Heat. | ||
LH = 16 |
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HH = 5 |
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Calculate: (228 X 16) + (350 X 5) = 5398 | ||
3648 ¬ 5398 ¬ 5600 ⇒ therefore calculate next cycle Low Heat run time. | ||
LHrun time = | 5600 − 5398 | = 1.6 ⇒ therefore during next cycle, unit will run for 2 minutes in Low Heat and then switch to High |
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Heat if a call for heat is still present.
EXAMPLE 2:
Furnace ran for 16 minutes in Low Heat and 10 minutes in High Heat. LH = 16
HH = 10
Calculate: (228 X 16) + (350 X 10) = 7148
7148 - 5600 ⇒ therefore next cycle will be initiated in High Heat. Low Heat run time is 0 minutes.
EXAMPLE 3:
Furnace ran for 13 minutes in Low Heat (LH) and 5 minutes in High Heat (HH). This will happen if control algorithm calculated maximum Low Heat run time be 13 minutes based on a previous cycle.
LH = 13
HH = 5
Calculate: (228 X 13) + (350 X 5) = 4714
3648 ¬ 4714 | ¬ 5600 ⇒ therefore calculate the next cycle Low Heat run time. | |
LHrun time = | 5600 − 4714 | = 7.26 ⇒ therefore unit will run for 7 minutes in Low Heat and then switch to High Heat if a call for |
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heat is still present.
EXAMPLE 4:
Furnace ran for 0 minutes in Low Heat and 10 minutes in High Heat. LH = 0
HH = 10
Calculate: (228 X 0) + (350 X 10) = 3500
3500 ¬ 3648 ⇒ therefore next cycle will be initiated in Low Heat up to 16 minutes maximum, then switch to High Heat if a call for heat is still present.
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