The flow rate necessary to deliver the full output of the heat source at a specific temperature drop can be found using equation below:

Q = H / (8.01 x ρ x c x ▲T)

Where:

• Q= Water volume flow rate (GPM)

• H = Heat load (Btu/hr)

• ▲T = Intended temperature drop (°F)

• ρ = Fluid's density at the average system temperature (lb/ft3)

• c = the fluid's specific heat at the average system temperature (Btu/lb/°F)

• 8.01 = a constant

In small to medium size hydronic systems, the product of (8.01 x ρ x c) can be taken as 500 for

water, 479 for 30% glycol, and 450 for 50% glycol. The total heat removed by air condition chilled-

water installation can thus be expressed as

H = 500 x Q x ▲T

Where

• H = total heat removed (Btu/h)

• Q = water flow rate (gal/min)

• ▲T = temperature difference ( 0F)

**Evaporator Flow Rate**

The evaporator water flow rate can be expressed as

Qe = Htons x 24 / T

Where

• Qe = Evaporator water flow rate (GPM)

• Htons = Air conditioning cooling load (tons)

• T = Temperature differential between inlet and outlet (°F)

**Condenser Flow Rate**

The condenser water flow rate can be expressed as

Qc = Htons x 30 / ▲T

Where

• Qc = Condenser water flow rate (GPM)

• Htons = Air conditioning cooling load (tons)

• ▲T = Temperature differential between inlet and outlet (°F)

Note the equation above assumes 25% heat of compression.

**CONDENSATE GENERATION**

Condensate generation in an air condition system where specific humidity before and after are known can be expressed as

Q Cond = Q air x W Lb / (SpV x 8.33)

Q Cond = Q air x W GR / (SpV x 8.33 x 7000)

Where

• Q Cond = Air Conditioning condensate generated (GPM)

• Q air = Air Flow Rate through the air-handling unit cooling c oil (Cu-ft / minute)

• SpV = Specific Volume of Air (Cu-ft per lb of dry air)

• W Lb = Specific Humidity diff. between inlet and outlet of air stream across coil (lb-H2O per

lb of dry air)

• W GR = Specific Humidity diff. between inlet and outlet of air stream acros s coil (Gr. H2O per lb of dry air)

**FLOW RATES IN HEATING SYSTEMS**

The volumetric flow rate in a heating system can be expressed by the basic equation:

Q = H / (Cp x ρ x ▲T)

Where

• Q = volumetric flow rate (GPM)

• H = heat flow rate (Btu/hr)

• CP = specific heat capacity (Btu/lb-°F)

• ρ = density (lb/ft3 )

• ▲T = temperature difference (°F)

The basic equation can be expressed for water with temperature 600F flow rate as:

Q = H (7.48 gal/ft3 ) / ((1 Btu/lb- 0F) (62.34 lb/ft3 ) (60 min/h)▲T)

Or

Q = h / (500 x ▲T)

Where

• Q = Water flow rate (GPM)

• H = Heat flow rate (Btu/hr)

• ▲T = Temperature difference (0F) (usually 20ºF)

For more exact volumetric flow rates for hot water the properties of hot water should be used.

Water Mass Flow Rate Water mas s flow can be express ed as:

m = h / ((1.2 Btu/lb- 0F) x ▲T)

Where

• m = mass flow (lb/hr)