Heating and Cooling Load Calculations and Energy Efficiency
This domain tests load estimation and the energy rules that follow it: design conditions, envelope transmission, solar and internal gains, ventilation and infiltration, diversity, and the efficiency limits of boilers, chillers and the envelope itself (Mabhas 19).
Building the load
Use site-specific design conditions, not generic ones: Iranian plateau summers commonly fall near 35–40 °C dry bulb with large daily swing, and winters near −5 to 0 °C depending on city. Transmission uses U-values limited by Mabhas 19; solar gain through glass often exceeds opaque-wall gain by an order of magnitude, so shading and glazing choice decide the peak. Ventilation and infiltration both add sensible and latent load - never count them twice, and take the larger, not the sum. Compute block load for plant and zone-by-zone peaks for terminals; diversity applies to the block figure only.
Worked example
A facade has 200 m² of opaque wall at U = 0.45 W/m²K with 20 K temperature difference: 200 × 0.45 × 20 = 1,800 W. The same facade holds 30 m² of glazing, effective SHGC 0.55, at 550 W/m² solar: 30 × 0.55 × 550 = 9,075 W. The glass carries five times the wall load; external shading cuts it at source, whereas thicker wall insulation would barely move the peak.
Efficiency and part load
Express chiller performance as kW/TR (COP = 3.517 / (kW/TR)) and use part-load values, because most hours are off-design. Boilers, chillers and fans carry energy labels; economisers, variable flow and reset schedules are the usual compliance measures. Insulate pipes and ducts to Mabhas 19 thicknesses and treat thermal bridges at balconies and slab edges.
Traps
Using indoor–outdoor ΔT for massive walls without a CLTD or RTS correction; adding infiltration on top of mechanical outdoor air; ignoring diversity; mixing COP with EER; quoting gross capacity while ignoring pump and fan energy.