Table II.

Parameters and Values for Energy and Cost Equations

Term	Definition	Value	Term	Definition	Value
ρa	Air density, kg m−3	1.225	Qtw	Total flow of wall fans, m3 s−1	0
ca	Specific heat of air, J kg−1 K−1	1005.4	Qtp	Total flow of pit fans, m3 s−1	0.823 (0.412,1.65)
Tr,	Room temperature, K	Computed in Eq. 1; initial value = 293	Qapc	Flow through contaminant control equipment (APC), m3 s−1	0, 0.236, 0.472, 0.944, 1.888
Tp	Pit temperature, K	Computed in Eq. 1; initial value = 293	rapc	Fraction of air in APC that is recirculated	0, 0.25, 0.5, 0.75, 1.0
Tf	Floor temperature, K	273.9	Qae	Airflow exchange ratio between pit and room air, m3 s−1	0.1×Qtp
Tg	Ground temperature, K	273.9	qgen	Heat generation rate, W	qheater + qlamps + qswine
To	Outside temperature, K	Eq. 3	qheater	Heat generation rate from 2 heaters, W	35166, when on
Tbias	Temperature bias to set median winter Temperature to test site in equation 3, K	278	qlamp	Heat generation rate from heating lamps (20 125-W lamps), W	2500
Arw,	Surface area of room-walls (including ceiling), m2	238.4	qswine	Heat generation rate from swine, W (Eq. 4)	11,254 (sow = 181.4 kg, piglet = 5.85 kg)
Arf	Surface area of floor, m2	54.6	Pelect	Electricity cost, $ / kWh	0.0536
Apw	Surface area of pit-walls, m2	146.464	Pgas	Natural gas cost, $ / m3	0.19
Urw	Heat transfer coefficient, room to wall, W m−2 K−1	0.286	Qheater	Natural gas consumption of 1 heater, m3 s−1	0.000472
Urf	Heat transfer coefficient, room to floor, W m−2 K−1	0.568	qfan	Pit fan power consumption, W	345
Upw	Heat transfer coefficient, pit to wall, W m−2 K−1	0.568	qapc	APC power consumption, W	Varies by APC; See Table 4
			Sheater	Switch function of heater, as determined by room temperature, per second	0 = off; 1 = on