**Related Resources: calculators**

### Building Sensible Heat Thermal Load with Air Exchange Calculator

Heat Transfer Engineering

Thermodynamics

HVAC Design and Engineering

Building Sensible Heat Thermal Load with Air Exchange Calculator

Outdoor air introduced into a building constitutes a large part of the total space-conditioning load, which is one reason to limit air change rates to the minimum required. Air exchange typically represents 20 to 50% of a modern, ventilation-code-compliant building’s thermal load in nontemperate climates. The effect on heating loads tends to be much larger than on cooling loads (McDowell et al. 2003).

Air exchange increases a building’s thermal load in several ways. First, incoming air must be heated or cooled from the outdoor air temperature to the indoor or supply air temperature. The rate of energy consumption by this sensible heating or cooling is

Eq. 1

*q _{s} = 60 · Q · ρ · c_{p}*

*·*ΔT

where

*q _{s}* = sensible heat load, Btu/h

Q = airflow rate, cfm

*ρ*= air density, lbm/ft

^{3}(about 0.075 at or near sea level)

*c*= specific heat of air, Btu/lbm·°F (about 0.24)

_{p}ΔT = temperature difference between indoors and outdoors, °F

and at or near sea-level air density, with an adjustment for typical room air humidity, this equation is commonly presented for design use as

Eq. 2

*q _{s} =* 1.1

*·*Q

*·*ΔT

Equations (1) and (2) are known as the sensible heat equation.

HVAC designers typically assume sea-level air pressure for locations with altitudes of 2000 ft or lower.

Related

- General Ventilation Rates Table
- Steady-State Indoor Air Quality Formulae and Calculator
- Accurate Heating and Cooling Load Calculations
- Air Conditioning Size Calculator and Estimator Chart This calculator is provided for use to calculate basic size in BTU to adequately cool a room of know size.
- Unit Thermal Resistances Well Sealed Air Spaces
- Air Conditioning System Design and Analysis Document This is an introduction to air conditioning systems (frequently referred to as HVAC systems – heating, ventilating and air conditioning systems).
- HVAC Heating Ventilation Air Conditioning
- HVAC Air Change Out Frequency (minutes) General recommendations for total volume of air change out for selected type indoor air spaces.
- Heat Transfer Practical Approach Leidenfrost effect

Source

2016 ASHRAE Handbook - HVAC Systems and Equipment, ASHRAE: 2016.