Document L1rYq6xq4zVxQJQ6a73V9abz

1238 CHAPTER 51 1958 Guide / When coils are installed in the floor slab, these systems must be operated continuously (day and night). Night setback is not desirable, but when used it must be placed on the room thermostats and the-setback must not exceed 10 deg.. Generally room temperatures, read on wall thermometers placed 60 in. from the floor, can be one to two deg lower than with other types of systems for equal comfort. Floor temperature must not exceed 85 F on design days except that a perimeter band, not exceeding 15 in. from the walls, may have a surface temperature of 100 F. Floor panels should not be expected to warm the large volumes of air required for school ventilation, and for this reason a tempered air supply is required in all except mild climates. MAINTENANCE AND OPERATION Controls, boilers and combustion equipment, fans and mechanical heat ing devices, traps and valves, all need attention at least annually. Every designer must use extreme care in selecting equipment that will require a minimum of attention, and see that it is accessible for service. While school custodial forces may be competent, they frequently have more work than can be handled during normal working hours. Unusual maintenance problems may therefore result in deterioration of equipment and systems. While first cost is important, final selection of equipment should not be made without consideration of the overall cost which in cludes maintenance and service. CHAPTER 52 INSTRUMENTS AND MEASUREMENTS Temperature Measurement, Pressure Measurement, Air Flow Measurement, Air Change Measurement, Humidify Measurement, Heat Transfer Through Building Materials, Evaluation of Thermal Environment, Combustion. Analysis, Smoke Density Measurements, Determination of Air Contaminants, Sound and Vibration Measurements - HEATING and air conditioning engineers and technicians require instruments for both laboratory and field use. Somewhat more pre cision is attainable and essential in the laboratory, where research and de velopment are undertaken, than in the field, where acceptance and adjust ment tests are conducted. Some instruments have attained an adequate state of development, while others fall far short of the desirable. For in stance, temperatures can now be measured readily with ample accuracy for most purposes, while a convenient and precise method for determining or comparing the dustiness of atmospheres is lacking, and improvement in existing hygrometers and humidity controllers is essential. Codes and standards covering different types of heating and air condi tioning devices and apparatus have been promulgated by various authori tative organizations, and instruments essential for performance or com pliance testing are enumerated in the relevant publications.1' 2-3'4 The present purpose is to discuss the use and characteristics of the more im portant instruments. TEMPERATURE MEASUREMENT6'6 Thermometers Any device capable of indicating temperature is a thermometer, but in common usage the term thermometer without qualification has come to signify the ordinary mercury-in-glass temperature indicating device. This type has a useful range from --40 F, the freezing point of mercury, to about 1000 F, at or near which the glass usually softens. Lower temperatures can be measured with alcohol-filled thermometers for which the range is ~ 94 F to +248 F. The better thermometers have their scales, either Fahrenheit or Centigrade, etched with acid into the glass which forms their stems. The probable error for etched stem thermometers is plus or minus one scale division, and calibration is desirable for much test work, thermometers are calibrated during manufacture at not less than two temperatures--the freezing and boiling points of water--and calibration 18 Accomplished with the instrument completely immersed in a bath ^nown temperature. The intervening scale divisions are then ap plied to the stem. When such a thermometer is used with the stem in completely immersed, a correction known as the stem correction is neces- 1239