Document 3epXMygJajBXRrmn8DD43Op8x

844 CHAPTER 38 1952 Guide reducing the house temperature 6 to 10 deg from about 10:00 pan. to 5:30 a.m.* In locating a room thermostat the following rules should be observed: 1. It should always be located towards the center of .a relatively open room on the coolest rather than the warmest side of the building. 2. It should never be mounted on an outside wall or other cold surface, or where it is exposed to cold drafts from an outside door. 3. It should never be mounted where it will be affected by direct rays of the sun; by heat from a nearby warm surface such as chimneys, pipes or ducts in a wall, or radiators; or by direct currents from a warm air register. 4. It should never be located where normal circulation of air is impeded by furni ture or an opened door. 5. It should be located where it is safe from mechanical injury. In a typical home, a satisfactory location for the thermostat can .usually be found on an inside wall of the living room or dining room. System Control There are several types of system control in common use for residential applications. They are usually of the two-position (on-off) type, or of the proportioning type. .1. Two-Position (On-Off) Control. The most simple type of domestic control is the type in which the room thermostat starts the burner or other source of heat when the temperature of the air at the thermostat falls below, the thermostat setting, and stops the source of heat when the.air temperature rises above the setting. If forced warm air or forced hot water is used, the fan or circulator may be turned on and off at approximately the same time as the source of heat. 2. Proportioning Control. When a proportioning type of control is used, the flame of the burner may be varied, or the burner may be cycled (started and stopped) frequently to provide for time modulation so that the heat input to the home is proportioned continuously to the heat loss from the home. The fan of a forced warm air system or the circulator of a forced hot water system may be run almost continuously, thereby providing for the constant flow of heat into the home. Such operation minimizes the cold drafts on the floor as caused by cold air dropping from cool walls and windows during the off period of an on-off system. Air-Conditioning Systems Year 'round residential air-conditioning systems which provide for heat ing in winter and cooling in summer should be given the same considera tion in selecting the control system as required for commercial air-con ditioning systems described later in this chapter, since the basic principles are the same and the final results must provide for the comfort of the occupants. Economy in first cost may result in both lack of economical operation and discomfort. ZONE CONTROL In residential heating, it is often desirable to divide the house into two or more zones for greater accuracy of control and comfort. Each zone may then be maintained individually at the desired' temperature level. The division by zones should be based upon exposure and occupancy; the most common division is usually found to be: 1. Living section such as living room, dining room, den. 2. Sleeping section. Save Fuel for Victory, University of Illinois, Engineering .Experiment Station Circular Series -No. 47, p. 31. Automatic Control 845 3. Service section such as kitchen, pantry, servant's quarters. 4. Recreational areas. Zone control for steam and hot water heating systems is employed where it is desired to control the heating effect of ,a multiplicity of radiators or convectors, located in various heated spaces, through the use of a single regulator. Under certain conditions, particularly in buildings of limited size, it is possible to consider the entire building as a single heating zone. In such cases, the zone regulator, or master controller, may operate, directly, the automatic firing equipment of the boiler or the reducing valve in the street steam main. In large buildings the demands of satisfactory tempera ture control, however, will make it necessary to sub-divide the heating system into suitable zones. There are a number of factors to be considered in zoning, in order that heating requirements-in a single zone will be approximately consistent throughout its extent. 1. Exposure may be a factor to be considered, with particular reference to pre vailing winds, sun effect, and the shelter afforded by surrounding structures and topographical features. 2. Occupancy may be a determining factor, in that the indoor temperature re quirements for the activities carried on in various portions of the building may vary, and the hours of occupancy likewise may differ. 3. The physical characteristics of the building will enter into the sub-dividing of the heating system into zones by reason of the fact that satisfactory temperature conditions throughout a single zone of given extent may not be enjoyed equally in buildings of dissimilar types of construction. Also, the height of the building and its horizontal extent and form are considerations which must be borne in mind. 4. The cost of the zone control equipment for such additional zones as might seem otherwise desirable, often will influence the decision as to the final number of zones to be employed. In buildings of considerable size, accepted practice dictates that there shall be at least one zone for each exposure, although each exposure very possibly should be sub-divided vertically into two or more zones, for the higher structures. Also, the presence of two or more wings, having the same generaTex posure, may suggest the desirability of more restrictive zoning. In smaller build ings, and in those of larger extent where cost and other conditions limit the number of zones, a common compromise is to combine the North and West exposures in one zone; and the East and South exposures in a second zone. Frequently, when the street floor level is given over to public spaces or to activities which are markedly different from, those carried on in the remainder of the building, it.is advisable to provide a separate steam main, with conventional room thermostats in each individ ual area. For steam heating systems, the radiator output may be varied pro. portionately to the changes in outdoor temperature, by any of a number of general methods. Those in most common use are: 1. Turning the steam on and off at appropriate intervals, as dictated by tempera ture or time considerations, proportioned to the need for heating. 2. Varying the pressure of steam in the system in accordance with the demand for heat. 3. Throttling the steam pressure, at the demand of the controller, to allow flow through orifices in proportion to the heating requirements. In hot water heating, the accepted practice is (1) to vary the tempera ture of the hot water supplied to the system, or (2) to vary the flow of hot water; both being varied proportionately to the heating requirements. The regulator, for each zone usually is of a type which in some manner responds to the outdoor temperature and effect of sun and wind for the