HVACPowDen 08a

Capacity and electrical demand

HVACPowDen 08a is  a program for quickly estimating the required capacity and electrical demand of cooling and heating equipment for 30 different building types in the 10 US climate zones.  Results are expressed in cooling tons, Btu/hr-ft2, total kW demand, and W/ft2.  Program is now integrated with HVACSysEff.xls.

Developed as part of an EPA-sponsored Energy Star Buildings project.

HVAC System Efficiency

Modern HVAC systems are increasingly complex and methods for comparing the SYSTEM cooling efficiency of various alternatives are not well established.  This program is a method for 1) summing the power requirements of all system components, 2) deducting cooling capacity for the heat input of interior auxiliary eqipment, and 3) computing the net SYSTEM efficiency using three common units of measure:  kW/ton, energy efficiency ratio (EER ≡ Btu/watt-hour), and Coefficient of Performance (COP ≡ WattThermal /WattElect).

The SYSTEM efficiency for a variety of HVAC types are computed in the worksheets in this program.  Results are shown below.  Typical default values for each component are used and they can be corrected in the corresponding worksheets.  Each system may include as few as three but as many as seven of the components listed below.

1. Chiller/Compressor (Input based on ASHRAE Std. 90.1-2004 COP values converted to kW/ton, corrected for fluid temperatures and flows)
2. Supply air handler (For fan motors > 1.0 horsepower, input based on cfm/ton, total pressure, motor and fan efficiencies, capacity deduct for power input to motor)
3. Return air fan (Input based ventilation air fraction, total pressure, motor and fan efficiencies, deduct for power input to motor corrected for ventilation air fraction)
4. Chilled water pump (Input based on gpm/ton, total head, motor and pump efficiencies, capacity deduct for power input to pumps)
5. Condenser water pump (Input based on gpm/ton, total head, motor and pump efficiencies, NO capacity deduct for power input)
6. Cooling tower fan (Input based on fan type, NO capacity deduct for power input)
7. Fan coil units or VAV terminal fans (For motors < 1.0 horsepower, input based on motor type and survey of fans watts per ton, deduct for power input to motor)

A technical discssion of this method for computing SYSTEM efficiency can be found in the ASHRAE publications HVAC Simplified (2006) or the ASHRAE Journal (July, 2003).