A 24-m3 direct heat-sink calorimeter with on-line data acquisition, processing, and control

Area of Science:

• Human thermoregulation
• Calorimetry
• Physiological measurement

Background:

• Accurate measurement of human heat loss is crucial for understanding thermoregulation.
• Previous calorimeters faced challenges with large volumes, response times, and stability.
• Direct heat-sink calorimeters offer potential for precise, continuous measurement.

Purpose of the Study:

• To construct and evaluate a large-volume (24-m3) direct heat-sink calorimeter.
• To assess its performance for continuous measurement of human evaporative and sensible heat loss.
• To validate its accuracy, stability, and response time for long-term human studies.

Main Methods:

• Construction of a 24-m3 direct heat-sink calorimeter.
• Implementation of real-time processing to compensate for physical time constants and delays.
• Calibration and performance testing for linearity, precision, stability, and response time.
• Conducting 25-hour continuous experiments with human subjects.

Main Results:

• The calorimeter demonstrated linear responses for evaporative (0-320 W) and sensible (0-280 W) heat loss with high precision.
• Excellent stability was achieved, with drift <0.6 W and low standard deviations over 24-72 hours.
• Fast response times (95% in 15 min) and independence from calibration source position were confirmed.
• No measurable cross-talk between heat loss types and negligible humidity dependency were observed.
• Human experiments showed no recorded discomfort during 25-hour trials.

Conclusions:

• The 24-m3 direct heat-sink calorimeter is a reliable instrument for continuous human heat loss measurement.
• Real-time processing effectively addressed stability and response-time issues in large-volume calorimeters.
• The calorimeter's performance characteristics support its use in extended human thermoregulation research.