ASHRAE Journal - September 2020 - 49

TECHNICAL FEATURE

reduction factor called the simultaneous coefﬁcient,
which is the quotient of the number of appliances in use
and the total number of appliances (Table 1).
Equation 2 describes total moisture emission in the
kitchen (kg/h):
W = W1 + W2 + W3

TABLE 1 Recommended values for simultaneous coefficient.3

(2)

where
W1 = Moisture emission from people, kg/h
W2= Moisture emission from kitchen appliances,
which are not equipped with exhaust hoods, kg/h
W3 = Moisture emission from outdoor air, kg/h
W2 can be found by using Tables 5A through 5F from
Reference 2 or Table A1 from Reference 5, in which the
data about speciﬁc moisture emissions from different
types of kitchen appliances is provided.

M ex = ∑ ( Loi ρi ) + Lgv ρgv

(3)

where
Loi = Exhaust volume airﬂow rate in the i th kitchen
exhaust hood or ventilated ceiling (can be
found by the calculation method described in
Reference 3), m3/h
Lgv = Volume airﬂow rate, exhausted by general
exhaust ventilation from the upper zone of the
kitchen, m3/h
ρi = Density of the air, exhausted by the i th kitchen
exhaust hood or ventilated ceiling, kg/m3
ρgv = Density of the air, exhausted by the general
exhaust ventilation from the upper zone of the
kitchen, kg/m3

Calculation of the Supply Airﬂow Rate
The amount of air exhausted from the kitchen should
be at least 10% higher than the airﬂow supplied to the
kitchen.3 The mass ﬂow rate (kg/h) that comes from the
adjacent spaces is deﬁned as following:
(4)
Mad = Lad ρad

SIMULTANEOUS COEFFICIENT K SIM

Hotel

0.6 - 0.8

Hospital

0.5 - 0.7

Cafeteria

0.5 - 0.7

School

0.6 - 0.8

Restaurant

0.6 - 0.8

Industrial

0.6 - 0.8

where
L ad = Volume airﬂow rate from the adjacent spaces,
m3/h
ρad = Density of the air that comes from the adjacent
spaces, kg/m3
The supply mass ﬂow rate Msup (kg/h) is estimated from
the air-balance equation for the kitchen as compensation the exhaust air:
(5)

M sup = M ex − M ad

Calculation of the Exhaust Airﬂow Rate
Exhaust mass ﬂow rate is described by Equation 3 as the
sum of exhaust airﬂow rates of exhaust hoods and general exhaust ventilation of the room (in the presence of
it) (kg/h):

KITCHEN TYPE

Calculation of the Air Parameters in the
Occupied Zone of the Kitchen
This algorithm of calculations is also described in
Reference 1. To calculate supply airﬂow rate in a commercial kitchen, we ﬁrst need to ﬁnd the process line
of the air parameters in this kitchen. The process line ε
(kJ/kg) is a quotient of total heat gains in the kitchen Q tot
and total moisture emission W:
ε=

3600Qtot
W

(6)

Calculation of ε for the commercial kitchen cannot be
precise, but using Equation 6 is an acceptable rough estimation. According to Reference 4, the value of ε varies from
5000 kJ/kg to 7000 kJ/kg (2,150 Btu/lb to 3,009 Btu/lb) during the maximum load of the kitchen equipment, depending upon the type of catering enterprise. To estimate the
ε value, it is acceptable to take the average value from this
range, which omits calculating moisture emissions.
The value of enthalpy (kJ/kg) of air in the occupied zone of
the kitchen is estimated from the energy balance equation:
hoz =

(3600Q

tot

+ M sup hsup + M ad had

)

M ex

(7)

where
hoz = Enthalpy of the supply air, kJ/kg
SEPTEM BER 2020

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ASHRAE Journal - September 2020

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