Question

a) What is the difference between latent and sensible heat gains in building cooling load analysis? Provide examples of each (2 marks) b) In heating load calculations, it is a normal practice to neglect the solar heat gain Explain why. (2 marks) c) An air conditioned single family detached house with a Figure_Q6A is located in Perth, Australia (Latitude 31° South). The ceiling height is 24 m. The summer floor plan shown in design indoor temperature is 25°C. Outside design conditions are 36.6°C dry bulb and 20.1°C wet bulb. Assume the daily range (DR) of 10°C. Using the RLF (Residential Load Factor) method, find the component cooling load through the external window of the Lounge The window is constructed froma low-e, low solar double-pane glass with Aluminium frames. Assume half fixed, half operable with insect screens. A 0.8 m eave overhang room (1.2 m height x 3.432 m) with eave edge 0.4 m higher than the top of the window is used. White roller shade is used for interior shading, assume half closed. (8 marks) d) Estimate the amount of natural gas (in m2) used to heat the home described in Qóa, for one year given the following information: (5 marks) Winter design heat loss is 12 kW at t (indoor air) 20°C and to (design outdoor air) 7.4°C Thermostat setting is maintained at 20°C The building has continuous intermal gains of 1.4 kW Average heater efficiency is 90% Heating value of natural gas is 10 kW-hr/m3 5720 3432 PORCH 2184 LOUNGE DINING NITCHEN 3432 1248 NTRY L'DRY W.C. EED 1 EED 2 EED 3 BATH 13730 mn Figure_Q6a Floor plan of the single family detached house. ww oc88

Answer 1

a)

Sensible heat -

Heat which a substance absorbs, and while its temperature goes up, the substance does not change state. Sensible heat gain is directly added to the conditioned space by conduction, convection, and/or radiation

Occupant’s body heat

Appliance & Light heat

Solar Heat gain through glass

Latent Heat -

heat gain when moisture is added to the space either from internal sources (e.g. vapour emitted by occupants and equipment) or from outdoor air as a result of infiltration or ventilation to maintain proper indoor air quality

  Moisture-laden outside air form Infiltration & Ventilation

Occupant Respiration & Activities

Moisture from Equipment & Appliances

b)

the heat load calculations are carried out assuming steady state conditions (no solar radiation and steady outdoor conditions) and neglecting internal heat sources.

credit for solar heat gain or internal heat gains is usually NOT included and the thermal storage effects of the building structure are generally ignored because the time at which the space may realize the heat gain as a cooling load will be considerably offset from the time the heat started to flow.