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PerformCalc™ - HVAC&R Performance Test  Updated 4/12/17   Provide inputs in the blue boxes, other inputs optional. 

The fields with the red border are required or invalid.
Return Air
Supply Air
Dry Bulb
Dry Bulb
Omit this input to have the supply air air calculated at the same moisture content as
the return air (calculated as saturated if equal moisture is not possible). Not available
when calculating airflow from remperature rise.
Power Factor can be measured
with certain meters or calculated
with a volt, amp and watt meter.
Typical Power Factor of a motor
iranges from 0.60 to 0.98
Electrically Commutated Motors
(ECM) and some 3 phase motors
have the lowest Power Factors.
Resistive heating elements
have a Power Factor of 1
Leave blank if the average Power
Factor (Pf) of the motor(s) is not
known. Power Factors of motors
range from 0.62 to 0.98
PSC motors have much a higher
Power Factor than ECM's or
inverter system motors.
Heating Fuel
The Barometric Pressure
reported by weather
stations is adjusted to sea
level and therefor not the
actual pressure at higher
elevations. Obtain actual
pressure or use Altitude.
sCFM is Standard CFM, density = 0.075 lbda/ft³. Measured specifically in dry air units of mass (pounds).
Use this when the entered airflow is obtained from charts, tables or equations representing or derived
from "Standard Air" conditions (typically 70°F dry air at sea level).
ᴀCFM is Actual CFM, the density varies with pressure, temperature and moisture content. Use this when
the entered airflow is measured at its actual density or directly from the actual velocity × area.
The entered CFM is converted to Actual (Moist/Dry) or Standard Air Specific (as selected by options below)
units of mass for the calculated outputs. Actual Dry Air Specific units are used as default.
Also, when calculating CFM from temperature rise, this is used to determine whether the result is displayed
as "Actual" or "Standard" CFM.
Leave blank to use
the default altitude
for the selected city
ft³/min
Used to determine if Electric Heat is energized by
comparing the Rated kW to the measured amperage.
The Power Factor for the electric heat portion of the
measured amperage is set to 1.
Static Pressures
Cost of fuel ($)
TESP: Total External Static Pressure. Measured entering and leaving
the furnace or fan/coil (air-handling) unit. Entering is negative and
Leaving is positive.
PD: Pressure Drop across coil. Measured entering and leaving the coil.
Both Entering and Leaving are positive.
Select areas of non-turbulent flow for measurements.
US Average Residentail
Jan. 2016 YTD
Btu's per fuel unit
US Projected Residentail Average 2016
0.964/Ccf, 9.64/Mcf and 0.96423/therm
updated 4/2016
/cf NG
US Average Residential Heating Oil
updated 4/2016
/gal Oil
US Average Residential Propane
updated 4/2016
/gal LP
Sets the default Altitude or Barometric
Pressure and Density Factor according
to the selected city. Also sets the
Full Load Heating and Cooling Hours
(EPA 2002 estimate).
When selected, results are calculated in units of the Total Air and
Water Vapor Mixture. This is used for the highest accuracy, it is necessary
for high temperatures and humidity. Otherwise, the results are calculated
in units of Dry Air and the moisture it could theoretically carry.
Dry Air Specific is commonly used for system design, and is what typical
psychrometric charts and common psychrometric applications use.
Also, it is used to select whether the measured ᴀCFM airflow input
is "Moist Air Specific" or "Dry Air Specific".
Uncheck if blower is not
in the measured air-stream
when calculating CFM from
temperature rise.
If checked, calculations will be made with Standard Dry Air
Specific units of mass, Density = 0.075 lbda/ft³ for both the
return and supply airflow. It overides the "Moist Air Specific"
option.
Psychrometer Type 
For calculations with wet bulb input.
Applies the Ferrel Psychrometric Equation ps`- pw =A∙p∙(t-t`)∙(1.00115∙t`)
to aspirated/sling or non aspirated psychrometers when "Wet Bulb"
temperature is used as a humidity input.
A = 0.000666 when wet-bulb is aspirated and not frozen
A = 0.000594 when wet-bulb is aspirated and frozen
A = 0.000799 when wet-bulb is non aspirated and not frozen
A = 0.00072 when wet-bulb is non aspirated and frozen
When "Electronic" is selected,
Wetbulb = the Thermodynamic wet bulb temperature (like a typical chart)
Select this to calculate aiflow (CFM) from the temperature rise
of an electric heater and/or motor in the air-stream.
The Supply Air humiidity input is grayed out and the supply air
is calculated to be at the same moisture content as the return
air (a motor or heater should not change the moisture level).

To find a systems current steady state capacity:

To calculate Btu's of dry air, provide dry bulb temperatures only, for moist air, add the return air humidity. To calculate changes in humidity include the supply air humidity as well. Provide airflow to convert Btu's per pound to Btu's per hour and to also calculate air conditioning and heat pump efficiencies when voltage and amperage are also entered.

 

To find the airflow of an air-handler or an electric furnace:

You can calculate CFM from the btu output of an electric heater and/or bower motor (airflow input must be blank), Provide dry bulb temperatures, volts and amps of the indoor air-handling unit. Add return air humidly for slightly higher accuracy. Assure the "Calculate Airflow from Electric Heat or Blower Motor Temperature Rise" check box is checked and "Electricity" from the "Heating Fuel" drop down list is selected.

With a well sealed unit and duct connections, matched thermometers & accurate static pressure measurements you can calculate CFM from the Temperature Rise of the blower motor only (must be in the airstream). All electrical power input is converted to sensible heat or a change in pressure (ultimately all of it is measurable energy).

 

This performance calculator takes a snapshot of the systems current operation and assumes steady state operation for one hour. Capacity, efficiency, fuel use and cost are based on the single set of inputs. It can be used for comparative purposes like before and after a repair for example.

Humidity inputs, if not entered will calculate the air as dry, or with the supply air at the same moisture content as the return air when possible.

This calculator illustrates the difference when using standard air factors such as, 1.08, 4.5, and 0.68, (0.075 lbda/ft³ and 0.24 Btu/ft³·°F) instead of the actual conditions.

For fossil fuel heating calculations; if the calculated input capacity at the efficiency percentage provided does not approximately match the rated input capacity on the nameplate, then the furnace may not be performing as rated. This could be due to altitude, nozzle size and/or fuel pressure changes.

 

Websites for current fuel costs

Natural Gas //eia.gov/outlooks/steo/tables/pdf/5btab.pdf To convert Dollars per Thousand Cubic Feet ($/Mcf) to Dollars per Hundred Cubic Feet ($/Ccf) , divide by 10. To convert Ccf to Therm multiply by 1.0002387672212

Heating Oil & Propane //205.254.135.7/petroleum/heatingoilpropane/

Electricity //www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_06_b

 

Websites for current Btu's per fuel unit

Natural Gas //eia.gov/dnav/ng/ng_cons_heat_a_EPG0_VGTH_btucf_m.htm

Distillate Fuel Oil & Propane //eia.gov/totalenergy/data/monthly/pdf/sec13_1.pdf To convert Million Btu per Barrel to Btu per Gallon, divide by 0.000042

 

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