|Frenz, Uwe - GERMAN INST OF HUMAN NUTR|
Submitted to: Thermochimica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 1996
Publication Date: N/A
Interpretive Summary: One problem that exists in the measurement of the amount of heat produced by an individual is the thermal inertia of the measurement device. All calorimeters for use with humans must contain furnishings to provide for a comfortable living environment. These furnishings by nature have the capacity to store heat. When a subject emits heat into the environment of the calorimeter some of the heat enters the furnishings and thereby escape detection by the instrument. This heat is released into the environment at a later date. In this paper we propose a method for estimating the amount and time course of this heat storage and release. This work impacts principally researchers since it improves our current method for estimating the amount of heat a person produces. However, in the long term the work will benefit the public through the development of better models of heat loss by people.
Technical Abstract: Direct calorimetry is used investigating combustion energy of fuels, thermic properties of materials and metabolic processes. Its results however may be influenced by the dynamic properties of the equipment, if it is not much faster than the subject. When performing direct calorimetry at living-beings the dynamic properties of the system chamber-interior-subject tmust be taken into account. A single compartment model is known to compensate for the dilution of metabolic gases in the chamber. Heat however is not simply diluted, it is stored in the chambers interior and the subject's body too. A two-compartment-model was shown to compensate heat storage in a furnished human calorimeter chamber. A model to estimate proper model parameter from calibration experiments was established. Alcohol combustion experiments resulted in 7.8 + 1.1% of the combusted heat measured after extinguishing the flame over periods of up to three hours. Using the two-compartment-model this was overcompensated to -1.6 + 1.9% within periods of less than 15 minutes. Humans or animals in the chamber would change the model parameter dramatically due to their hugh heat capacity. Corresponding parameter could not be derived from only a few calibration experiments, more work will be done in the future.