R1.. = thermal resistivity in the separate wall/construction layers (m2K/W)
Ro = thermal resistivity surface outside wall (m2K/W)
For walls and floors against earth (6) - can be modified to
1 / U = Ri + R1 + R2 + R3 + .. + Ro + Re (6b)
where
Re = thermal resistivity of earth (m2K/W)
The heat loss due to ventilation without heat recovery can be expressed as:
Hv = cp ρ qv (ti - to) (7)
where
Hv = ventilation heat loss (W)
cp = specific heat air (J/kg K)
ρ = density of air (kg/m3)
qv = air volume flow (m3/s)
ti = inside air temperature (oC)
to = outside air temperature (oC)
The heat loss due to ventilation with heat recovery can be expressed as:
Hv = (1 - β/100) cp ρ qv (ti - to) (8)
where
β = heat recovery efficiency (%)
An heat recovery efficiency of approximately 50% is common for a normal cross flow heat exchanger. For a rotating heat exchanger the efficiency may exceed 80%.
Due to leakages in the building construction, opening and closing of windows, etc. the air in the building shifts. As a rule of thumb the number of air shifts is often set to 0.5 per hour. The value is hard to predict and depend of several variables - wind speed, difference between outside and inside temperatures, the quality of the building construction etc.
The heat loss caused by infiltration can be calculated as
Hi = cp ρ n V (ti - to) (9)
where
Hi = heat loss infiltration (W)
cp = specific heat air (J/kg/K)
ρ = density of air (kg/m3)
n = number of air shifts, how many times the air is replaced in the room per second (1/s) (0.5 1/hr = 1.4 10-4 1/s as a rule of thumb)
V = volume of room (m3)
ti = inside air temperature (oC)
to = outside air temperature (oC)
Heating systems - capacity and design of boilers, pipelines, heat exchangers, expansion systems and more.
Thermal resistance in building elements like walls, floors and roofs above and below the ground.
The heat emission from a radiator or a heating panel depends on the temperature difference between the radiator and the surrounding air.
Classification of heat recovery efficiencies - temperature efficiency, moisture efficiency and enthalpy efficiency - online heat exchanger efficiency calculator.
Calculating steam and condensate loads in steam heated systems.
Required hot water expansion volume in open, closed and diaphragm tanks.
Estimated infiltration heat losses from buildings.
Calculate heat emission from column and panel radiators.
Steam radiators and steam convectors - heating capacities and temperature coefficients.
Heat loss through common building elements due to transmission, R-values and U-values - imperial and SI units.
Water condensation on inside glass windows surfaces vs. outside temperature and inside temperature and humidity.
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