Chillers, Heat Pumps & Thermal Storage

Chillers, Heat Pumps & Thermal Storage · Study · PE Mechanical: HVAC and Refrigeration · FE → PE Prep

Key equations

Cooling COP

\text{COP} = \dfrac{\dot Q_L}{\dot W}

Dimensionless; cooling effect $\dot Q_L$ over compressor input $\dot W$ , both in the same units. Convert Btu/h to W with $3.412\ \text{Btu/h}=1\ \text{W}$

Ton of refrigeration

1\ \text{ton} = 12{,}000\ \text{Btu/h} = 3.516\ \text{kW}

The conversion that links every chiller rating; from §4 Thermodynamics ( $3{,}516\ \text{W}$ per ton).

kW/ton to COP

\text{kW/ton} = \dfrac{3.516}{\text{COP}}

Inverse efficiency — lower is better. $3.516$ is kW of heat per ton. Typical water-cooled $0.5\text{–}0.6$ , air-cooled $1.0\text{–}1.2$

EER definition

\text{EER} = \dfrac{\dot Q_L\,[\text{Btu/h}]}{\dot W\,[\text{W}]}

EER from kW/ton and COP

\text{EER} = \dfrac{12}{\text{kW/ton}} = 3.412\,\text{COP}

The 12 is $12{,}000\ \text{Btu/h}$ per ton divided by 1000 W; the $3.412$

IPLV in kW/ton (linear approximation)

\text{IPLV} \approx 0.01\,A + 0.42\,B + 0.45\,C + 0.12\,D

Linear weighted sum of kW/ton at 100/75/50/25% load ( $A,B,C,D$

IPLV — AHRI 550/590 form

\text{IPLV} = \dfrac{1}{\dfrac{0.01}{A}+\dfrac{0.42}{B}+\dfrac{0.45}{C}+\dfrac{0.12}{D}}

Condenser approach

\text{Approach}_{\text{cond}} = T_{\text{cond,sat}} - T_{\text{cw,leaving}}

Evaporator approach

\text{Approach}_{\text{evap}} = T_{\text{chw,leaving}} - T_{\text{evap,sat}}

Condenser heat rejection

\dot Q_{\text{rej}} = \dot Q_L + \dot W

Condenser water flow

\text{gpm} = \dfrac{\dot Q_{\text{rej}}}{500\,\Delta T}

D. Condensers/Evaporators

Chiller Performance: kW/ton, COP, EER and IPLV

COP is the dimensionless truth; everything else is a unit choice

kW/ton — the chiller-plant currency

EER and the 12,000-Btu/h-per-ton bridge

IPLV — chillers spend their lives at part load

Water-cooled vs air-cooled — why the condenser sets the efficiency

Approach: the heat-exchanger penalty at both ends

Exam strategy

Key equations

Worked examples

Common pitfalls

References

Heat-Pump Balance Point and Heating COP

Condensers: Water-Cooled, Air-Cooled and Evaporative

Evaporators and Variable Refrigerant Flow (VRF)

Chilled-Water and Ice Thermal Storage Sizing