HVAC and refrigeration calculators.Heat loads, airflow, ducts, refrigerant, psychrometrics, F-gas and system checks.

Air heat loads

Air heat loadsSensible heat in an air stream (Q = ρ cp q ΔT)

Q = ρ c_{p} \dot{V} Δ T

Air heat loadsLatent heat from a moisture content difference

Q_{L} = ρ \dot{V} \frac{| W_{1} - W_{2} |}{1000} h_{fg}

Air heat loadsRoom cooling load from internal and solar gains (simple)

Q_{sen} = \frac{N q_{s} + L_{p} A + E_{p} A + A_{g} g I}{1000}

Heat loss

Heat lossFabric heat loss through an element (Q = U A ΔT)

Q = U A (t_{i} - t_{e})

Heat lossVentilation heat loss from air change rate (0.33 n V ΔT)

Q = 0.33 n V (t_{i} - t_{e})

Airflow and ducts

Airflow and ductsAirflow from air change rate

q_{h} = n V

Airflow and ductsCircular duct area and air velocity

A = \frac{π D^{2}}{4000000}

Airflow and ductsRectangular duct area and air velocity

A = \frac{a b}{1000000}

Airflow and ductsEquivalent diameter of a rectangular duct (Huebscher)

D_{e} = \frac{1.30 {(a b)}^{0.625}}{{(a + b)}^{0.25}}

Airflow and ductsStraight duct pressure drop (Darcy–Weisbach with Colebrook)

v = \frac{\dot{V}}{\frac{π D^{2}}{4000000}}

Fans

FansFan affinity laws (change of speed)

Q_{2} = Q_{1} (\frac{N_{2}}{N_{1}})

FansFan power from flow, pressure and efficiency (and SFP)

P_{air} = \dot{V} Δp

Psychrometrics

PsychrometricsSaturation vapour pressure of water (ASHRAE Hyland–Wexler and Magnus)

T = t + 273.15

PsychrometricsMoisture content (humidity ratio) from relative humidity

p_{ws} = 0.61094 \cdot \exp (\frac{17.625 \cdot t}{t + 243.04})

PsychrometricsRelative humidity from moisture content

p_{w} = \frac{p W}{621.945 + W}

PsychrometricsDew point temperature from temperature and RH (Magnus)

γ = \ln (\frac{RH}{100}) + \frac{17.625 t}{243.04 + t}

PsychrometricsSpecific enthalpy of moist air

p_{w} = \frac{RH}{100} \times 0.61094 \cdot \exp (\frac{17.625 \cdot t}{t + 243.04})

PsychrometricsWet-bulb temperature from temperature and RH (Stull)

a_{1} = \arctan (0.151977 {(RH + 8.313659)}^{0.5})

PsychrometricsMixing of two air streams (adiabatic)

v_{1} = \frac{0.287042 (t_{1} + 273.15) (1 + 1.607858 \frac{W_{1}}{1000})}{p}

Capacity units

Capacity unitsCooling or heating capacity: kW to BTU/h and tons of refrigeration

B = \frac{1000 \times P}{0.29307107}

Capacity unitsCooling or heating capacity: BTU/h to kW and tons of refrigeration

P = \frac{B \times 0.29307107}{1000}

Capacity unitsCooling capacity: tons of refrigeration to kW and BTU/h

P = TR \times 3.5168528

System checks

System checksSuperheat from suction line temperature

SH = T_{line} - T_{sat}

System checksSubcooling from liquid line temperature

SC = T_{sat} - T_{liq}

System checksSaturation temperature from pressure (interpolate your P-T data)

T = T_{1} + (P - P_{1}) \frac{T_{2} - T_{1}}{P_{2} - P_{1}}

F-gas

F-gasCO₂ equivalent of a refrigerant charge (F-gas)

{CO}_{2} e = \frac{m \times GWP}{1000}

F-gasF-gas leak-check frequency (GB)

{CO}_{2} e = \frac{m \times GWP}{1000}

Installation

InstallationAdditional refrigerant charge for pipe length

W = \max (L_{A} r_{A} + L_{B} r_{B} - D, 0)

InstallationStrength and tightness test pressures (BS EN 378-2)

P_{s 1} = 1.1 \times PS

InstallationNitrogen purge volume and time

V_{p} = \frac{π}{4} {(\frac{d}{1000})}^{2} L \times 1000

InstallationRefrigerant pipe velocity check

A = \frac{π}{4} {(\frac{D}{1000})}^{2}

Performance

PerformanceCOP or EER from capacity and power input

COP = \frac{Q}{P}

PerformanceCarnot (ideal) COP from evaporating and condensing temperatures

{COP}_{c} = \frac{T_{e} + 273.15}{T_{c} - T_{e}}

PerformanceRefrigeration capacity from mass flow and enthalpy change

Q = \dot{m} (h_{1} - h_{4})

PerformanceRefrigerant mass flow from capacity

\dot{m} = \frac{Q}{h_{1} - h_{4}}

PerformanceCompressor swept volume and volumetric efficiency

V_{s} = \frac{π}{4} {(\frac{D}{1000})}^{2} \frac{S}{1000} z N \times 60

PerformanceCondensate flow from a cooling coil

{\dot{m}}_{w} = \frac{Q_{L}}{h_{f g}} \times 3600

BS EN 378 charge limits

BS EN 378 charge limitsMaximum charge for an occupied space (concentration limit × room volume)

m_{\max} = RCL \times V

BS EN 378 charge limitsFlammable refrigerant room charge limit (BS EN 378-1 Annex C)

m_{\max} = 2.5 \times {LFL}^{1.25} h_{0} \sqrt{A}

Superheat by refrigerant

Superheat by refrigerantR-32 superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-410A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-454B superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-134a superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-407C superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-404A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-22 superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-290 superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-600a superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-744 superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-1234yf superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-1234ze(E) superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-448A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-449A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-452A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-513A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-407A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-417A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-422D superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-454C superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-455A superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Superheat by refrigerantR-717 superheat from suction pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerant

Subcooling by refrigerantR-32 subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-410A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-454B subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-134a subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-407C subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-404A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-22 subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-290 subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-600a subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-744 subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-1234yf subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-1234ze(E) subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-448A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-449A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-452A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-513A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-407A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-417A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-422D subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-454C subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-455A subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Subcooling by refrigerantR-717 subcooling from liquid line pressure

P_{abs} = P_{g} + P_{atm}

Fault diagnosis

Fault diagnosisRefrigerant circuit fault diagnosis (superheat and subcooling)

Δ SH = SH - {SH}_{t}

HVAC and refrigeration calculators.Heat loads, airflow, ducts, refrigerant, psychrometrics, F-gas and system checks.

Air heat loads

Heat loss

Airflow and ducts

Fans

Psychrometrics

Capacity units

System checks

F-gas

Installation

Performance

BS EN 378 charge limits

Superheat by refrigerant

Subcooling by refrigerant

Fault diagnosis

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