Metabolic Load Analysis
3.1 Metabolic Load:
The metabolic activities inside human body constantly create heat and humidity (i.e. perspiration). This heat passes through the body tissues and is finally released to the cabin air. This amount is considered as a heat gain by the cabin air and is called the metabolic load. The metabolic load can be calculated by
Qmet = Σ MADU
Passengers
Where M is the passenger’s metabolic heat production rate.
(It is assumed from ISO 8996 based on various criteria for driver: M = 85 W/m2, Passenger: M = 55 W/m2)
Here, ADU is the estimation of the body surface area,
ADU = 0.20(W)0.425 (H)0.725
(W and H are weight and height; For average: W = 70kg, H = 1.75m)
ADU = 0.20(70)0.425 (1.75)0.725
ADU = 1.85 m2
Qmet = Σ MADU
= 85 …show more content…
As the passengers breathe, the amount of CO2 concentration linearly increases over time. Thus, a minimum flow of fresh air should be supplied into the cabin to maintain the passengers comfort. Arndt and Sauer reported the minimum fresh air requirements for different numbers of passengers in a typical vehicle. For instance, a minimum of 13% fresh air is needed for a single passenger. For a small sedan car at a pressure difference of 10 Pa, a leakage of 0.02 m3/s was reported. Because of the air conditioning and ventilation, the cabin pressure is normally slightly higher than the ambient. Thus, the ventilation load has to take the leakage air flow rate into account. Meanwhile, in the steady-state operation, the built- up pressure is assumed to remain constant. Hence, ambient air is assumed to enter the cabin at the ambient temperature and relative humidity, and the same flow rate is assumed to leave the cabin at the cabin temperature and relative humidity. According to psychrometric calculations, ventilation heat gain consists of both sensible and latent loads. To account for both these terms, assuming a known flow rate of fresh air entering the cabin, the amount of thermal heat gain can be calculated …show more content…
The mathematical formulation of the model can thus be summarized as
Qtotal = Qmet + Qair + QDif + QRef + QAmb + QExt + QEng + Qventilation
= 564.25 + 1058.5 + 1720.38 + 150.24 + 352.8 + 161.48 + 259.75 + 63.03
= 2782.43 W
AC Load: The duty of the air conditioning system is to compensate for other thermal loads so that the cabin temperature remains within the acceptable comfort range. In cold weather conditions, positive AC load (heating) is required for the cabin. Inversely, in warm conditions, negative AC load (cooling) is needed for maintaining the comfort conditions. The actual load created by the AC system depends on the system parameters and working conditions. In this work, it is assumed that an AC (or heat pump) cycle is providing the thermal load calculated by
QAC = - [Qtotal]
= - (maca + DTM) (Ti - Tcomf) /tc
[Here, Tcomf is target comfort temperature, tc is overall pull down temperature,
tc can be defined as the temperature required for
The metabolic activities inside human body constantly create heat and humidity (i.e. perspiration). This heat passes through the body tissues and is finally released to the cabin air. This amount is considered as a heat gain by the cabin air and is called the metabolic load. The metabolic load can be calculated by
Qmet = Σ MADU
Passengers
Where M is the passenger’s metabolic heat production rate.
(It is assumed from ISO 8996 based on various criteria for driver: M = 85 W/m2, Passenger: M = 55 W/m2)
Here, ADU is the estimation of the body surface area,
ADU = 0.20(W)0.425 (H)0.725
(W and H are weight and height; For average: W = 70kg, H = 1.75m)
ADU = 0.20(70)0.425 (1.75)0.725
ADU = 1.85 m2
Qmet = Σ MADU
= 85 …show more content…
As the passengers breathe, the amount of CO2 concentration linearly increases over time. Thus, a minimum flow of fresh air should be supplied into the cabin to maintain the passengers comfort. Arndt and Sauer reported the minimum fresh air requirements for different numbers of passengers in a typical vehicle. For instance, a minimum of 13% fresh air is needed for a single passenger. For a small sedan car at a pressure difference of 10 Pa, a leakage of 0.02 m3/s was reported. Because of the air conditioning and ventilation, the cabin pressure is normally slightly higher than the ambient. Thus, the ventilation load has to take the leakage air flow rate into account. Meanwhile, in the steady-state operation, the built- up pressure is assumed to remain constant. Hence, ambient air is assumed to enter the cabin at the ambient temperature and relative humidity, and the same flow rate is assumed to leave the cabin at the cabin temperature and relative humidity. According to psychrometric calculations, ventilation heat gain consists of both sensible and latent loads. To account for both these terms, assuming a known flow rate of fresh air entering the cabin, the amount of thermal heat gain can be calculated …show more content…
The mathematical formulation of the model can thus be summarized as
Qtotal = Qmet + Qair + QDif + QRef + QAmb + QExt + QEng + Qventilation
= 564.25 + 1058.5 + 1720.38 + 150.24 + 352.8 + 161.48 + 259.75 + 63.03
= 2782.43 W
AC Load: The duty of the air conditioning system is to compensate for other thermal loads so that the cabin temperature remains within the acceptable comfort range. In cold weather conditions, positive AC load (heating) is required for the cabin. Inversely, in warm conditions, negative AC load (cooling) is needed for maintaining the comfort conditions. The actual load created by the AC system depends on the system parameters and working conditions. In this work, it is assumed that an AC (or heat pump) cycle is providing the thermal load calculated by
QAC = - [Qtotal]
= - (maca + DTM) (Ti - Tcomf) /tc
[Here, Tcomf is target comfort temperature, tc is overall pull down temperature,
tc can be defined as the temperature required for