Technical Note: Temperature and Humidity Control in Indirect Calorimeter Chambers

A three-chamber, indirect calorimeter has been a part of the Environmental Laboratory at the U.S. Meat Animal Research Center (MARC) for over 25 years. Corrosion of the animal chambers and unreliable temperature control necessitated either major repairs or complete replacement. There is a strong demand for heat production measurements; therefore, a new four-chamber calorimetry system was designed and constructed. The objective of this article is to describe the design of the calorimeters, including the chambers, heating and cooling systems, and animal penning system, verify the proper gas sampling techniques, and document the environmental control system. The chambers are both temperature and humidity controlled, with air-handling units contained within each animal chamber to reduce air leak potential. The temperature and humidity controllers are both capable of cyclic and constant patterns within a nominal range. A total of 264 calorimetry runs were conducted to verify the temperature and humidity control with the four calorimeter chambers. These measurements were used to test the environmental controls (dry bulb and dewpoint temperatures). A total of 14 heat production verification runs were completed on the four calorimeters to verify the indirect calorimetry system and ensure that the chambers are airtight. Environmental control of the four calorimeters was very good, and only small changes to the protocol were identified that could improve the overall performance of the system. The heat production verification runs showed an O2 error of less than 1.5% and a CO2 error of less than 1.0%, thus ensuring that the system is airtight and functioning correctly as an indirect calorimeter.