Mass Flow Rate and Re-circulated Room Air
1. Air in a room is at 220C d.b. and RH = 60%. Find the following conditions from the psychrometric chart: specific volume, dew point, specific enthalpy, wet-bulb temperature and moisture content.
2. Outdoor air at 0 0C d.b. and 100% saturation is heated with a low-pressure hot-water battery to 30 0C d.b. Identify all the condition data for both entry and exit states.
3. Re-circulated room air at 21°C d.b., 50% saturation is mixed in equal amounts with summer outdoor air at 31°C d.b., 22 °C w.b. State the condition of the mixed air.
4. An air-handling unit receives re-circulated room air at 23 °C d.b., 50% saturation and a flow rate of 2 m3/s, and fresh air at -5 °C d.b., 100% saturation with a flow rate of 0.5 m3/s. The mixed air is heated to 35 °C d.b. Identify each condition point and calculate the rate at which energy has to be supplied in kW.
5. Calculate the rate at which energy has to be supplied in kW when air is heated from 10 °C
d.b., 8 °C w.b. to 40 °C d.b. when the inlet air volume flow rate is 3 m3/s. Use the inlet specific volume to calculate the air mass flow rate.
6. A cooling coil has an air-inlet condition of 29 °C d.b., 21.8°C w.b. and an air-outlet state of
13°C d.b., 90% saturation. Calculate the cooling rate in kW when the inlet air flow to the coil is 4m3/s.
7. A single-duct air-conditioning system takes 1.5 m3/s of external air at -3 °C d.b., 80% saturation and mixes it with 5 m3/s of re-circulated room air at 20 °C d.b., 50% saturation.
The mixed air is heated to 32 .C d.b. prior to being supplied to the rooms. Calculate the rate at which energy has to be supplied in kW.
8. Outside air at -5 °C d.b., 80% saturation enters a preheater battery and leaves at 24 °C d.b.
The fresh-air inlet volume flow rate is 2 m3/s. Find the outdoor-air wet-bulb temperature and specific volume, the heated-air moisture content and percentage saturation. Calculate the rate at which energy has to be supplied in kW.
2. Outdoor air at 0 0C d.b. and 100% saturation is heated with a low-pressure hot-water battery to 30 0C d.b. Identify all the condition data for both entry and exit states.
3. Re-circulated room air at 21°C d.b., 50% saturation is mixed in equal amounts with summer outdoor air at 31°C d.b., 22 °C w.b. State the condition of the mixed air.
4. An air-handling unit receives re-circulated room air at 23 °C d.b., 50% saturation and a flow rate of 2 m3/s, and fresh air at -5 °C d.b., 100% saturation with a flow rate of 0.5 m3/s. The mixed air is heated to 35 °C d.b. Identify each condition point and calculate the rate at which energy has to be supplied in kW.
5. Calculate the rate at which energy has to be supplied in kW when air is heated from 10 °C
d.b., 8 °C w.b. to 40 °C d.b. when the inlet air volume flow rate is 3 m3/s. Use the inlet specific volume to calculate the air mass flow rate.
6. A cooling coil has an air-inlet condition of 29 °C d.b., 21.8°C w.b. and an air-outlet state of
13°C d.b., 90% saturation. Calculate the cooling rate in kW when the inlet air flow to the coil is 4m3/s.
7. A single-duct air-conditioning system takes 1.5 m3/s of external air at -3 °C d.b., 80% saturation and mixes it with 5 m3/s of re-circulated room air at 20 °C d.b., 50% saturation.
The mixed air is heated to 32 .C d.b. prior to being supplied to the rooms. Calculate the rate at which energy has to be supplied in kW.
8. Outside air at -5 °C d.b., 80% saturation enters a preheater battery and leaves at 24 °C d.b.
The fresh-air inlet volume flow rate is 2 m3/s. Find the outdoor-air wet-bulb temperature and specific volume, the heated-air moisture content and percentage saturation. Calculate the rate at which energy has to be supplied in kW.