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ASHRAE 55 Thermal Comfort Tools

Thermal Comfort Tools have been developed in recent years to help with the calculations to bring a residential or commercial building into compliance with ASHRAE Standard 55. These comfort tools are either downloadable software or used online.

ASHRAE Standard 55 has been in existence since 1966. It is based on Fanger's PMV index (a predictive rating scale), the most recognized model in thermal comfort research. It can be found also in international Standards such as Europes EN 15251 and ISO 7730 and China's GB/T 50785. ANSI/ASHRAE Standard 55-2013, Thermal Environmental Conditions for Human Occupancy, specifies conditions for acceptable thermal environments and is intended for use in design, operation, and commissioning of buildings and other occupied spaces. The 55 Standard is used for commercial and residential spaces.

The key components of compliance with Standard 55 can be broken up into three parts: personal factors, general factors and local factors.

Personal
The two personal factors are metabolic rate and clothing values. These values are easily selected from tables in the Standard or from the pull down menus in the ASHRAE Thermal Comfort Tool or the online software tool developed by the Center for the Built Environment. There is no calculation required for these items. Raters simple state what they believe the representative occupant will be doing for an activity and what the occupant will be wearing.

General
The general factors are air temperature, mean radiant temperature (MRT), humidity and air speed. Of these, air temperature and humidity are simply stated values if controlled (i.e. thermostats and humidistats settings when connected to HVAC systems) and require no calculation.

The MRT can be calculated with one of three different methods. Two of the three are simple formulas. The third should be done using the ASHRAE Thermal Comfort Tool (see image below).

Air speed comes down to airflow calculations, duct design, register (diffuser) selection and placement.

Local
When occupants are at low activity such as sitting down for dinner, working in the home office or lying on the couch watching TV; and wearing for example, light pajamas or light sweat pants, designers must consider local discomfort factors of temperature stratification, radiant asymmetry, floor temperatures and draft. (See article by Robert Bean, R.E.T., P.L. for further explanation)

ASHRAE Thermal Comfort Tool

ASHRAE's Thermal Comfort Tool software provides a user-friendly interface for calculating thermal comfort parameters and making thermal comfort predictions using several existing thermal comfort models. ASHRAE Thermal Comfort Tool, Version 2 maintains consistency with ANSI/ASHRAE Standard 55-2010 and can be used to comply with USGBC's LEED®.

Four-Model System
This updated interface includes four models, including the new PMV with Elevated Air Speed, used to automatically make use of the SET air speed model described in section 5.2.3.2 of the standard. Input parameters consist of environmental conditions (air temperature, mean radiant temperature, air velocity and humidity), activity level and clothing. Results include PMV, PPD, Humidity and an indicator of compliance with Standard 55. A green check mark indicates compliance and a red X indicates non-compliance with each factor, with an overall indicator in the Compliance box. Additional comments are provided when relevant.

Mean Radiant Temperature Calculator
A significant new feature allows the user to calculate mean radiant temperature (MRT) based on surface temperatures of a rectangular room. The user can specify the overall size of the room (width, length and height), the location of the occupant, and the temperatures of each surface. A rectangular window or panel can be placed on each surface (walls, floor and ceiling) and can be given a different temperature than the surface it is placed on. This can be used to represent any surface that is warmer or colder than the wall, including windows, heating panels, cooling panels, or even equipment.

Clo Calculator
An improved interface to the clothing calculator was developed to allow more flexibility for an increased clothing library. The new interface allows the user to create an ensemble of clothing made up of a combination of individual elements. The data for the Clo calculator is provided in a text file that can be easily updated in the future.

CBE Thermal Comfort Tool

Another comfort tool available for evaluating comfort according to ASHRAE Standard-55 is a free online tool developed by Center for the Built Environment (CBE). CBE developed a number of features that are important for practitioners: (a) ability to compare two or three thermal comfort scenarios (compare tool); (b) ability to plot how the comfort area changes in the psychrometric chart when clothing, metabolic activity, air velocity or mean radiant temperature are varied within a given range (range tool).

The end users are allowed to upload a weather file in EnergyPlus format (.epw) or comma-separated values (CSV) format to calculate the running average temperature for the adaptive comfort model. We will also enable the CSV import/export of the results.

The CBE Thermal Comfort Tool will be continuously updated based on any approved changes to ASHRAE 55 Standard 55-2013.

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