PE HVACR: Know off the Dome

$$Q_{sensible}=?$$

Air: $Q_{s}=1.1\cdot CFM\cdot\Delta T\cdot DF$

Water: $Q_{w}=500\cdot GPM\cdot\Delta T$

Generic: $Q_{}=\dot{m}\cdot c_{p}\cdot\Delta T$

$$Q_{latent}=?$$

Air: $Q_{l}=4840\cdot CFM\cdot\Delta W\cdot DF$

Generic: $Q=\dot{m}_{}\cdot h_{fg}$

$$Q_{total}=?$$

Air: $Q_{T}=4.5\cdot CFM\cdot\Delta h\cdot DF$

Generic: $Q=\dot{m}\cdot\Delta h$

$$\rho_{air}=?$$

STP: $\rho_{air}=0.075\frac{lbm}{ft^3}$

$$\rho_{water}=?$$

STP: $\rho_{water}=62.4\frac{lbm}{ft^3}$

1 ft³ = ? gal

1 ft³ = 7.48 gal

1 gal water = ? lbm water

1 gal water = 8.34 lbm water

$$COP=?$$

Cooling: $COP=\frac{Q_{evaporator}\left\lbrack btuh\right\rbrack}{W_{compressor}\left\lbrack btuh\right\rbrack}$

$$EER=?$$

Cooling:$EER=\frac{Q_{evaporator}\left\lbrack btuh\right\rbrack}{W_{compressor}\left\lbrack watts\right\rbrack}$

From COP: $EER=COP\cdot3.412$

$$\frac{kW}{ton}=?$$

From EER: $\frac{kW}{ton}=\frac{12}{EER}$

1 Refrigeration Ton = ? Btu/h

1 Refrigeration Ton = 12,000 Btu/h

1 Watt = ? Btu/h

1 kW = ? Btu/h

1 Watt = 3.412 Btu/h

1 kW = 3412 Btu/h

$$HP_{mechanical}=?_{}$$

Fan: $HP_{fan}=\frac{CFM\cdot inch_{H2O}}{6356}$

Pump: $HP_{pump}=\frac{GPM\cdot ft_{head}}{3960}$

The power produced by the equipment (fan or pump).

$$HP_{brake}=?$$

$$HP_{brake}=\frac{HP_{mechanical}}{\eta_{equipment}}$$

The power leaving the motor shaft to turn the equipment (fan or pump).

$$HP_{electrical}=?$$

$$HP_{electrical}=\frac{HP_{brake}}{\eta_{motor}}$$

1 HP = ? W

1 HP = ? kW

1 HP = 746 W

1 HP = 0.746 kW

1 HP = ? Btu/h

1 HP = 2545 Btu/h

$$\epsilon=?$$

$$\epsilon=\frac{Q_{actual}}{Q_{\max}}$$

$$SHR=?$$

$$SHR=\frac{Q_{sensible}}{Q_{total}}$$

$$psia=?$$

$$psia=psig+P_{atm}$$

STP: $P_{atm}=14.7$$psia$

Lever Rule = ?

Dry Bulb Temperature: $DB_{mix}=DB_1\cdot\%CFM_1+DB_2\cdot\%CFM_2$

Humidity Ratio: $W_{mix}=W_1\cdot\%CFM_1+W_2\cdot\%CFM_2$

Enthalpy: $h_{mix}=h_1\cdot\%CFM_1+h_2\cdot\%CFM_2$

Does NOT work for Wet Bulb Temperature

% Relative Humidity = ?

$$\%RH=\frac{P_{v,actual}}{P_{v,saturated}}$$

Quality = ?

By Enthalpy: $x=\frac{h_{actual}-h_{f}}{h_{g}-h_{f}}$

By Mass: $x=\frac{m_{vapor}}{m_{vapor}+m_{liquid}}$

Compressor Efficiency = ?

$$\eta_{compressor}=\frac{h_{ideal,leaving}-h_{entering}}{h_{actual,leaving}-h_{entering}}$$

$h_{ideal,leaving}$ is the enthalpy of the refrigerant at the leaving compressor pressure (discharge pressure) after following the constant entropy line from the entering compressor pressure (suction pressure).

$${}^{\circ}R={}?$$

$${}^\circ R = {}^\circ F + 460$$

“Adiabatic”

$$\Delta h=0$$

Process follows constant enthalpy lines on psychrometric chart.

$$h_{superheated}=?$$

$$h_{superheated}=h_{saturated,vapor}+c_{p,vapor}\cdot\Delta T_{superheat}$$

$$h_{subcooled}=?$$

$$h_{subcooled}=h_{saturated,liquid}-c_{p,liquid}\cdot\Delta T_{subcool}$$

“Thermal conductivity”, $k$

A measure of how well a material promotes heat transfer.

Units: $\frac{Btu}{hr\cdot ft\cdot^{\circ}F}$ or $\frac{Btu\cdot in}{hr\cdot ft\cdot^{\circ}F}$

“Resistance”, $R=?$

A material’s ability to resist heat, accounting for the material’s thickness.

$$R_{conductive}=\frac{t}{k}$$

$R_{surfacefilm\left(convective+radiation\right)}=\frac{1}{h_{convective}+h_{radiation}}$ , combination accounted for in Handbook Surface Film Coefficients

$U=?$ …pull from previously made flashcards

$$U=\frac{1}{R}$$

$$U=\frac{k}{t}$$

Units: