Question

Question 1 Discuss, using diagrams where appropriate, how the annual domestic thermal load is calculated and how the heating and cooling loads can differ between countries. Total 10 marks. Question 2 Discuss the international standards relevant to conducting an LCA Total 10 marks. Question 3 Using an appropriate example discuss battery selection, performance and setup in PV systems. Total 10 marks. Question 4 Providing relevant numerical data, discuss some of the ways in which hydropower systems can be categorised Total 10 marks. Question 5 Discuss (using diagrams where appropriate) possible generators modes of operation and how this effects the generator speed.

Answer 1

QUESTION 1

• To estimate the required cooling or heating capacities, one has to have information regarding the design indoor and outdoor conditions, specifications of the conditioned space (such as the occupancy, activity level, various appliances and equipment used etc.) and any special requirements of the particular application.
• The design outdoor conditions are chosen based on design dry bulb and coincident wet bulb temperatures for peak summer or winter months for cooling and heating load calculations.
• Heating or Cooling Load Calculation: Design takes into account all the loads experienced by a building under a specific set of assumed conditions.

If we have all the data with us then we can further proceed as follows:

BRIEF EXPLANATION

STEP 1: Use of psychrometric chart to know the weight or density of the sytem on the basis of data collected (Indoor and outdoor conditions)

STEP 2: External loads Calculation:

a) Heat transfer rate through the walls:   Q_wall = U_wallA_wallETD_wall

where, Effective Temp. Difference (ETD)

b) Heat transfer rate through roof: Q_roof = U_roofA_roofETD_roof

c) Heat transfer rate through floor: Q_floor = U_floorA_floorETD_floor

d) Heat transfer rate through glass:   Q_glass = A_glass [U_glass(To−Ti)+SHGF_maxSC]

where, Solar Heat Gain (SHG) of glass

Internal Shading Coefficient (SC) of glass:

e) Heat transfer due to infiltration

Sensible heat transfer rate due to infiltration,Q_{s,inf :} Q_s,inf = m_infc_pm(To−Ti)

Latent heat transfer rate due to infiltration Q_l,inf: Q_l,inf = m_infh_fg(Wo−Wi)

STEP 3: Internal loads:

a) Load due to occupants:

Q_s,occ = no.of occupants x SHG

Q_l,occ = no.of occupants x LHG

b) Load due to lighting: Lighting load x floor area

c) Load due to appliance:

Q_{s appliances} = (Installed wattage ) x (Usage.wattage ) x CLF

Q_l,appliance   = (Installed wattage ) .(Latent heat fraction)

Total sensible and latent loads are obtained by summing-up all the sensible and latent load components (both external as well as internal)

Q_total = Q_s,total + Q_l,total

As calculation is based on various surrouding condition so heating and cooling load can differ between countries.