NIST SP 811 Appendix B.9: Heat Flow Rate conversion factors

Overview

This record rests on Appendix B.9, Heat Flow Rate, in the 2008 edition of NIST Special Publication 811 (the Guide for the Use of the SI) prepared by Ambler Thompson and Barry N. Taylor. The section gives conversion factors between units of heat flow rate. The library holds it as the source for the refrigeration ton value and as a basis for preliminary sustainability calculations.

The record's single fact is this: one refrigeration ton, defined as 12,000 Btu IT per hour, converts to 3,516.853 W (3.516853 kW) using the published NIST conversion precision. It is the basic constant used to bridge equipment catalogues that give cooling capacity in US units and electrical and thermal calculations that work in SI units.

In practice the factor is used in two directions: cooling capacity given in tons is multiplied by 3.516853 to convert to kW, while a heat load in kW is divided by the same number to convert to tons. The same constant also serves when converting between expressions of chiller plant efficiency (kW per ton and kW per kW).

As a limitation, the source is only a conversion constant; it says nothing about equipment performance, climate or load conditions. The record notes that product-specific data are explicitly labelled proxies when applied to generic equipment.

Key points

1. One refrigeration ton is defined as 12,000 Btu IT per hour.
2. At NIST's published conversion precision, one refrigeration ton equals 3,516.853 W.
3. The same value is expressed as 3.516853 kW.
4. The source is NIST SP 811 Appendix B.9, Heat Flow Rate.
5. The document was prepared by Ambler Thompson and Barry N. Taylor and dates from 2008.
6. Product-specific data are explicitly labelled proxies when applied to generic equipment.

Using it in design

• Use a single constant when converting cooling capacity between tons and kW: 1 ton = 3.516853 kW.
• Convert catalogue values given in tons to SI units before comparing them with heat load calculations.
• Use the same constant when converting chiller plant efficiency (kW per ton) to kW per kW, and state the conversion in the report.

Who should read it

Mechanical and energy engineers converting between US and SI units in cooling capacity and efficiency calculations.

Publication details

Authors

Ambler Thompson; Barry N. Taylor

Publisher

NIST

Year

2008

Document language

English

Source type

Government / public

Access

Citation only

DOI

10.6028/NIST.SP.811e2008

Licence

Bibliographic reference only — the document is not redistributed here; confirm reuse terms at the original source

Citation