---
tags:
  - type/encyclopedia-entry
title: HVAC Calculations
up: "[[electrical-construction]]"
---
# 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>

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

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

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

### Ton of Refrigeration (TR or TOR)

Unit of **power**

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

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

### Cubic Feet per Minute (CFM)

Unit of **volumetric flow**.

## Measures

### Airflow

External static pressure (ESP)
measured in inches of water (IN WC) "water column inches"

### 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.

##### Ratings

* MERV
* SEER2
* HSPF2

### Efficiency

* η (eta)

* ISMRE
