HVAC Systems and Control

Tutorial 3 (Lecture 5)

Engineering Mechanics Department

Q1:

In an auditorium which is to be maintained at a temperature not exceeding 24 oC and a relative humidity not exceeding 60 %, a sensible heat load of 132 kW and 78 kg/h of moisture has to be removed. Air is supplied to the auditorium at 18 oC.

(a)How many kg of air per hour must be supplied?

(b)What is the dew point temperature of supply air and what is the relative humidity?

(c)How much latent heat is picked up in the auditorium?

(d)What is the sensible heat factor?

Q2:

Given for the air conditioning of a room;

Room conditions: 26.5 oC DBT and 50 % RH

Room sensible heat gain = 26.3 kW

Room sensible heat factor = 0.82

Find:

(a)The room latent heat gain

(b) The apparatus dew point

(c)The cmm of air if it is supplied to the room at the apparatus dew point.

(d)The cmm and specific humidity of air if it is supplied to the room at 18 oC.

Q3:

Moist air at 31 oC dry bulb, 22 oC wet bulb and 1013.25 mbar barometric pressure flows over a cooler coil and leaves it at a state of 10 oC dry bulb and 7.95 g.w.v/kg d.a.

(a)If the air is required to offset a sensible heat gain of 2.5 kW and a latent heat gain of 0.35 kW in a room being air-conditioned, calcualate the mass of dry air whuch must be supplied ot the room in order to maintain a dry-bulb temperature of 23.5 oC inside.

(b) What will be the relative humidity in the room.

(c)If the sensible heat gain is diminished by 1.75 kW but the latent heat gain remains unchanged, at which temperature and moisture content must the air be supplied to the room?

Q4:

Given:

Room conditions: 26 oC DBT, 19 oC WBT

Outside conditions: 35 oC DBT, 27 oC WBT

Room heat gains:

Sensible heat = 11.1 kW

Latent heat = 3.9 kW

The conditioned air supplied to the room is 50 cmm and contains 25 % fresh air and 75 % recirculated room air. Determine:

(a)The DBT and WBT of supply air.

(b) The DBT and WBT of mixed fresh and recirculated air before the cooling coil.

(c)The apparatus dew point.

(d) The refrigeration load on the cooling coil and the moisture removed be the coil.

Q5:

The air-handling unit of an air-conditiong plant is supplied a total of 4500 cmm of dry air which comprises by weight 20 % fresh air at 40 oC DBT and 27 oC WBT and 80 % recirculated air at 25 oC DBT and 50 % RH. The air leaves the cooling coil at 13 oC saturated state.

Calculate the total cooling load and room heat gain.

Q6:

An air-conditioned space is maintained at 27 oC DBT and 50 % RH. The ambient conditions are 40 oC DBT and 27 oC WBT. The space has a sensible heat gain of 14 kW. Air is supplied to the space at 7 oC saturated.

Calculate:

(i)Mass of moist air supplied to the space in kg/h

(ii) Latent heat gain of space in kW

(iii)Cooling load of the machine in kW if 30 % of the air supplied to the space is fresh, the remainder being recirculated.

HVAC systems and control Associate Prof.Dr.Eng. M.S. Abd-Elhady Page1