Question

. If you know the difference in enthalpy (h) of the supply air and the room air, how could you use this to determine the required amount of supply air to condition for a heat loss or a heat gain?

What are the two preferred ways to supply air into a perimeter space to heat and cool the space?

What is the appropriate name for a residential hot air heating unit?

Answer 1

The sensible heat in a heating or cooling process of air (heating or cooling capacity) can be calculated in SI-units as

hs = cp ρ q dt          (1)

where

hs = sensible heat (kW)

cp = specific heat of air (1.006 kJ/kg oC)

ρ = density of air (1.202 kg/m3)

q = air volume flow (m3/s)

dt = temperature difference (oC)

Or in Imperial units as

hs = 1.08 q dt      (1b)

where

hs = sensible heat (Btu/hr)

q = air volume flow (cfm, cubic feet per minute)

dt = temperature difference (oF)

The reheat box function is used to heat the cold air flowing into the room when the room thermostat is calling for heat. The volume cannot be too low or the air supplied will be too warm and buoyant, and will not mix well with the air in the space, resulting in discomfort and possibly inadequate ventilation in the occupied zone

The majority of North American households depend on a central furnace to provide heat. A furnace works by blowing heated air through ducts that deliver the warm air to rooms throughout the house via air registers or grills. This type of heating system is called a ducted warm-air or forced warm-air distribution system. It can be powered by electricity, natural gas, or fuel oil.