Convective Heat Gain Electric Appliances

Related Resources: heat transfer

Convective Heat Gain Electric Appliances

Convective Heat Gain from Unhooded Electric Appliances During Idle (Ready-to-Cook) Conditions

The average rate of appliance energy consumption can be estimated from the nameplate or rated energy input qinput by applying a duty cycle or usage factor F_u. Thus, sensible heat gain q_s for generic electric, steam, and gas appliances installed under a hood can be estimated using one of the following equations:

q_s = q_input F_u F_R

q_s = q_input F_L

where F_L is the ratio of sensible heat gain to the manufacturer’s rated energy input. However, ASHRAE research (Swierczyna et al. 2008, 2009) showed the design value for heat gain from a hooded appliance at idle (ready-to-cook) conditions based on its energy consumption rate is, at best, a rough estimate. When appliance heat gain measurements during idle conditions were regressed against energy consumption rates for gas and electric appliances, the appliances’ emissivity, insulation, and surface cooling (e.g., through ventilation rates) scattered the data points widely, with large deviations from the average values.

The tables below lists usage factors, radiation factors, and load factors based on appliance energy consumption rate for typical electrical, steam, and gas appliances under standby (idle or ready-to-cook) and cooking conditions, hooded and unhooded.

Appliance	Energy Rate, Btu/h		Rate of Heat Gain, Btu/h				Usage Factor FU	Radiation Factor FR
Appliance	Rated	Standby	Sensible Radiant	Sensible Convective	Latent	Total	Usage Factor FU	Radiation Factor FR
Cabinet: hot serving (large), insulated^a	6,800	1,200	400	800	0	1,200	0.18	0.33
Cabinet: hot serving (large), uninsulated	6,800	3,500	700	2,800	0	3,500	0.51	0.20
Cabinet: proofing (large)^a	17,400	1,400	1,200	0	200	1,400	0.08	0.86
Cabinet: proofing (small 15-shelf)	14,300	3,900	0	900	3,000	3,900	0.27	0.00
Cheesemelter^b	8,200	3,300	1,500	1,800	0	3,300	0.41	0.45
Coffee brewing urn	13,000	1,200	200	300	700	1,200	0.09	0.17
Drawer warmers, 2-drawer (moist holding)^a	4,100	500	0	0	200	200	0.12	0.00
Egg cookerb	8,100	850	200	650	0	850	0.10	0.26
Espresso machine*	8,200	1,200	400	800	0	1,200	0.15	0.33
Food warmer: steam table (2-well-type)	5,100	3,500	300	600	2,600	3,500	0.69	0.09
Freezer (small)	2,700	1,100	500	600	0	1,100	0.41	0.45
Fryer, countertop, open deep fat^b	15,700	1,500	700	800	0	1,500	0.09	0.47
Griddle, countertop^b	27,300	6,100	2,900	3,200	0	6,100	0.22	0.48
Hot dog roller^b	5,500	4,200	900	3,300	0	4,200	0.77	0.22
Hot plate: single element, high speed	3,800	3,400	1,100	2,300	0	3,400	0.89	0.32
Hot-food case (dry holding)^a	31,100	2,500	900	1,600	0	2,500	0.08	0.36
Hot-food case (moist holding)^a	31,100	3,300	900	1,800	600	3,300	0.11	0.27
Induction hob, countertop^b	17,100	0	0	0	0	0	0.00	0.00

Appliance	Energy Rate, Btu/h		Rate of Heat Gain, Btu/h				Usage Factor FU	Radiation Factor FR
Appliance	Rated	Standby	Sensible Radiant	Sensible Convective	Latent	Total	Usage Factor FU	Radiation Factor FR
Microwave oven: commercial	5,800	0	0	0	0	0	0.00	0.00
Oven: countertop conveyorized bake /finishing^b	17,100	13,500	2,500	11,000	0	13,500	0.79	0.18
Panini^b	6,100	2,300	700	1,600	0	2,300	0.37	0.29
Popcorn popper^b	2,900	400	100	300	0	400	0.14	0.24
Rapid-cook oven (quartz-halogen)^a	41,000	0	0	0	0	0	0.00	0.00
Rapid-cook oven (microwave/convection)^b	19,400	3,900	300	3,600	0	3,900	0.20	0.08
Reach-in refrigerator^a	4,800	1,200	300	900	0	1,200	0.25	0.25
Refrigerated prep table^a	2,000	900	600	300	0	900	0.45	0.67
Rice cooker^b	5,300	300	50	250	0	300	0.05	0.17
Soup warmer^b	2,700	1,300	0	200	1,100	1,300	0.49	0.00
Steamer (bun)^b	5,100	700	100	600	0	700	0.13	0.16
Steamer, countertop^b	28,300	1,200	0	800	400	1,200	0.04	0.00
Toaster: 4-slice pop up (large)	6,100	3,000	200	1,400	1,000	2,600	0.49	0.07
Toaster: contact (vertical)^b	8,900	2,600	600	2,000	0	2,600	0.29	0.24
Toaster: conveyor (large)	32,800	10,300	3,000	7,300	0	10,300	0.31	0.29
Toaster: small conveyor^b	6,000	5,800	1,200	4,600	0	5,800	0.98	0.21
Tortilla grill^b	7,500	3,600	900	2,700	0	3,600	0.47	0.25
Waffle iron^b	9,200	900	200	700	0	900	0.10	0.22

Sources:

Swierczyna et al. (2008, 2009); with the following exceptions as noted.
^a Swierczyna et al. (2009) only.
^b Additions and updates from ASHRAE research project RP-1631 (Kong and Zhang 2016; Kong et al 2016).

References

ASHRAE Handbook of Fundamentals, 2021 Inch-Pound Edition