vault backup: 2025-10-08 18:16:15

hvac-calculations.md

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+---
+id:
+aliases: []
+tags: []
+---
+# 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)