---
id:
aliases: []
tags:
  - destiny/permanent
  - status/incomplete
  - topic/electrical
  - type/encyclopedia
title: HVAC Calculations
---
# HVAC Calculations

## Units

### British Thermal Unit

Unit of heat energy

There are several definitions of the Btu,
HVAC uses the IT definition,
abbreviated Btu<sub>IT</sub>

$$
\begin{align*}
1 \text{Btu}_\text{IT} &= \left( 4.1868 \times 453.59237 \times{\frac{5}{9}} \right) \text{J} \\
&\approx 1055.056 \text{J}
\end{align*}
$$

More common than Btu itself is
thousand British thermal units per hour (MBH),
a unit of power.

$$
\begin{align*}
1 \text{MBH} &= 1000 \text{Btu/hr} \\
&\approx 3.412 \text{W}
\end{align*}
$$

### Ton of Refrigeration (TR or TOR)

Unit of power

> [!info] Also Known As
> * refrigeration ton (RT)
> * ton (refrigeration)

$$
\begin{align*}
1 \text{TR} &= 12000 \text{Btu}_\text{IT}/\text{h} \\
&\approx 3516.853 \text{W}
\end{align*}
$$

### Cubic Feet per Minute (CFM)

Unit of volumetric flow

## Measures

### Airflow

* CFM

External static pressure (ESP)
measured in inches of water

### Heating/Cooling Capacity

* Tons (refrigeration)
* MBH

Entering air temperature (EAT)
Leaving air temperature (LAT)
Mixed air temperature (MAT)

Latent heat
Sensible heat

Sensible -> dry bulb
Latent -> wet bulb

#### ???

OSA EAT (F)
EXH EAT (F)

IN S.L.
OUT ALT.

### Efficiency

* η (eta)