BS2 Tutorial ans
- 1. Tutorial 1 Q1. What is Ventilation and why do we need ventilation in confined dwelling? Ventilation - a process of changing air in an enclosed space where fresh air keep replacing a proportion of withdrawn air within. Ventilation - a means of changing the air in an enclosed space to: • Provide fresh air for respiration - approx. 0.1 to 0.2l/s per person. • Preserve the correct level of oxygen in the air - approx. 21%. • Control carbon dioxide content to no more than 0.1%. • Concentrations above 2% are unacceptable as carbon dioxide is poisonous to humans and can be fatal. • Control moisture - relative humidity of 40% to 60% is acceptable. • Remove excessheat frommachinery,people, lighting, etc. • Dispose of odours,smoke, dust and other atmospheric contaminants. • Relieve stagnation and provide a sense of freshness - air movement of 0.15to 0.5 m/s is adequate. Q2 What do you understand by ‘rate of air change’ in ventilation? Rate of air change is the ratio of fresh air supplied each hour to the volume of the enclosed space. The calculation of rate of air change is m3/hour divide bythe total volume of an enclosed space. Normally the fresh air supplyis 30-35 m3 per person per hour and 17.5 m3 of air is required byeach person in every house in a house. In a living room with a space of 45 m3, there is 1.5 air changes for 4 family members each hour. By formula N = Q/V where N is the rate change per hour Q is the quantity of rate (m3/s) V is the volume of room space.
- 2. Note that the Q is in m3 per second whereas the N is per hour Q3 What are the potential consequences of extreme humidity levels? High levels of humidity within the home can have adverse effects for the occupants as well as the dwelling itself. Hygiene, health, retention of value, aesthetics and comfort are all areas which can be affected by a failure to maintain an optimal level of relative humidity. Q4 What are the ideal optimal indoor relative humidity range that will prevent potential adverse effects for occupants and the dwelling itself? If you are referring to one of my charts in the lecture note ventilation 1the range is 30% to 100% (blue in colour). Note that this chart is based on the Environment Canada's website (see below chart). Let us take the source from the Roger Greeno'stextbook which relative humidity is from40% to 60%
- 3. Q5 How does heat losses from our body? Q6 Ventilation design Question Using Equal velocity method, find the size of duct A & B and fan rating. Air velocity is selected throughout the system (duct A & B) is 5m/sGiven Q, the quantity of air is equally extracted through each grille. Q = Room volume xair changes per hour
- 4. Tutorial 2 Q1 a) Refrigerant A non-corrosive liquid or gas used in air conditioning to exchange heat. b) Compressor Single or multi stage centrifugal, reciprocating by piston action or rotaryto develop a compression of the refrigerant has. c) Expansion valve Control refrigerant flow into evaporator, excessive cause flooding and damage d) Condenser It is heat rejectersof the cycle. It is a device or unit used to condense a substance from its gaseous to its liquid state, by cooling it. e) Evaporator To evaporate from liquid to gas while absorbing heat in the process. Refrigerant are substances used to transfer heat and create a cooling effect bychanging state at specific temperature A compressor is a machine used to withdraw the heat laden refrigerant vapour from the evaporator, compress it fromthe evaporator pressure to the condensing pressure and push it to the condenser. Expansion valve controls the amount of refrigerant flow into the evaporator and restricts flow of high pressure refrigerant therefore lowering refrigerant pressure
- 5. A condenser is a device or unit used to condense a substance from its gaseous to its liquid state, bycooling it. In so doing, the latent heat is given up bythe substance, and will transfer to the condenser coolant. At the evaporator, the refrigerant liquid is converted to gas, absorbing the heat from the air in the room. This heat is then carried by the refrigerant from the evaporator as a low-pressure gas through a hose or line to the low side of the compressor, where the whole refrigeration cycle is repeated. The evaporator removes heat from the area that is to be cooled. Q2 Sketch a diagram showing a typical single stage vapour compression cycle and absorption refrigeration cycle. Q3 A room 15mx 7m x2.8m high is to have a ventilation rate of 11 air changes per hour. Air enters from a duct at a velocity of 8.5m/s. Find the air volume flow rate to the room and the dimensions of the square duct. Given Q =N xV Where Q is the air volume flow rate to the room N is air changes per hour
- 6. Given also Q = A x ʋ Where Q is the air volume flow rate to the room A is the duct cross sectional area ʋ is the velocity of air Q4 The air handling unit consists of several components such as filter, cooling coil, heating coil, humidifier and fan. State the function of each of the components Q5 Discuss the advantages and disadvantages of VAV system.