VAV Terminal Units
VAV with Electric Heater
Standard Model: VAV – PID – EH
Electric heating coils are applied on VAV terminal units as terminal reheat devices. Electric heat coil capacity is rated in kilowatts (kW). Coils are available with the total capacity divided into one, two or three stages.
Product Description
Operating Principle
Electric heating coils are applied on VAV terminal units as terminal reheat devices. Electric heat coil capacity is rated in kilowatts (kW). Coils are available with the total capacity divided into one, two or three stages.
Electric heat coils are available in single-phase or three-phase models. This refers to the type of power source connected to the coil. Single-phase models have resistance elements internally connected in parallel.
The current drawn for the electric coil will depend whether it is single phase coil or a three phase coil. The current drawn is necessary for determining what size wire should be used to power the electric coils and how big the primary power fusing should be.
Equation
The equations for current draw for these coils are:
1 ꝕ amps = kW x 1000 / Primary Voltage
3 ꝕ amps = kW x 1000 / Primary Voltage x 3
It is important to note that these coils have certain minimum airflow rates for each amount of kW heat the coils can supply to operate safely. These airflow values are based upon a maximum rise across the electric heat coil of 50°F (28°C).
The equation that relates the airflow across an electric coil to the temperature rise and the coil change in temperature is:
CFM = kW x 3145 / ΔT
Where:
CFM = Minimum airflow rate across the coil
kW = The heating capacity of the electric coil
3145 = A constant.
ΔT = The maximum rise in air temperature across the coil (usually 50°F (28°C))