Thermist

Thermist offers calculation software for professional HVAC engineers, with equations and data sourced from ASHRAE and NIST. Once necessary data is inputted, outputs are automatically calculated and displayed. Experiment with different inputs to see for yourself!

Notable features:

• Calculate adaptively with any sufficient set of inputs.
• Switch easily between inch-pound (IP) and metric (SI) units.
• Conveniently open optional popup mode.
• Customize all inputs through advanced settings.
• Share or save calculations seamlessly for any set of inputs.
• Accurately compute pressure drop by iteratively solving the Colebrook equation, paired with the Darcy equation, as recommended in ASHRAE Fundamentals.

Duct Sizer

Similar to a manual spinning "ductulator", this ductwork sizing tool solves for pressure drop, velocity, and/or duct size based on user inputs. By default, the calculator works with round sizes unless a rectangular dimension is inputted. Rectangular ductwork utilizes the equation credited to Heubscher to determine equivalent round ductwork size for pressure drop calculations, per ASHRAE fundamentals Duct Design chapter. Flat oval ductwork utilizes the equation credited to Heyt and Diaz to determine equivalent round ductwork size for pressure drop calculations, per ASHRAE fundamentals Duct Design chapter. For all duct shapes, velocity is calculated based on the actual duct free area.

Advanced setting enables the flat oval ductwork sizing plus gives the option for custom inputs for material roughness, elevation, and temperature. Elevation and temperature are used to determine viscosity and air density using ISO 2533:1975, the ideal gas law, and the 1985 NIST journal regarding properties of air. Viscosity and air density are used in pressure drop calculations. When sizing rectangular or flat oval ductwork, the + button can be clicked to view additional sizes meeting inputted criteria. If only size is inputted, alt size areas and equivalent round dimensions meet or exceed inputted size.

Inputs, outputs, and IP units:

• Airflow is the volumetric rate of air passing through ductwork. CFM is equal to cubic feet per minute.
• Pd is pressure drop that occurs to the airstream for straight duct runs only, not including fittings. In. wc/100' is equal to inches of water column per 100 feet of ductwork.
• Velocity is the volumetric speed of the airflow. Fpm is equal to feet per minute.
• Diameter is the dimension for round ductwork in inches.
• Height and width are dimensions for rectangular ductwork in inches.
• Aspect ratio is width:height ratio.
• Major and minor axis are dimensions for flat oval ductwork in inches. In advanced settings, change shape from default Rnd/Rect to Rnd/Oval for oval ductwork sizing.

Pipe Sizer

This pipe sizing tool is for HVAC non-gravity hydronic system sizing. Density and viscosity of water is interpolated based on NIST sourced data. Density and viscosity of glycol mixtures are interpolated based on Dow Chemical's DOWFROST/DOWTHERM data, which are referenced in ASHRAE Fundamentals. Advanced setting allows factoring in glycol plus gives the option for custom inputs for material roughness and fluid temperature. Internal pipe diameter assumes copper type L (per ASTM B88) for pipes NPS 2 or smaller and schedule 40 steel (per ANSI B36.10) for pipes NPS 2-1/2 and larger.

Inputs, outputs, and IP units:

• Flow is the volumetric flow rate of liquid passing through piping. Gpm is equal to gallons per minute.
• Pd is pressure drop that occurs to the liquid for straight pipe runs only, not including fittings. Ft. wc/100' is equal to feet of water column per 100 feet of piping.
• Velocity is the volumetric flow speed of the liquid. Fps is equal to feet per second.
• NPS is nominal pipe size in inches.

Steam Pipe Sizer

This pipe sizing tool is for HVAC saturated steam system sizing. Sizing is applicable wher condensate does not hnhibit flow of steam. Density and viscosity of steam is interpolated based on NIST sourced data. Advanced setting allows custom material roughness input. Internal pipe diameter assumes schedule 40 steel (per ANSI B36.10) for all pipe sizes.

Inputs, outputs, and IP units:

• Pressure is the guage pressure of the steam passing through piping. Psig is equal to pounds per square inch guage.
• Flow is the flow rate of steam passing through piping, by weight. Lbs/hr is equal to pounds of steam per hour.
• Pd is pressure drop that occurs to the steam for straight pipe runs only, not including fittings. Psi/100' is equal to pounds per square inch per 100 feet of piping.
• Velocity is the volumetric flow speed of the steam. Fpm is equal to feet per minute.
• NPS is nominal pipe size in inches.

Disclaimer

Thermist software is provided "as is" and is to be used only as a reference. While we endeavor to provide accurate calculations, we make no warranties or representations of any kind concerning the accuracy, reliability, suitability, or completeness of any of the contents or data provided. Users are advised to always cross-check results against other sources or calculations, understand and verify all input data before using it in any critical applications, and recognize that the performance of the software might vary based on various factors.