Document p8r55QvG1ox1xBMYLXz3az5d

54 iCXMKSIM I TAM* CHAPTER 4 1962 Guide And Data Book * Jo provide timdttsneou* hodmg and coaling with fixed refrigerant circuit. Suitable for centrifugal compressors end other factory assembled fluid coders. Fig. 2 .... Air-to-Liquid Heat Pump Cycle* . The well water can be supplied directly to the condenser and chiller instead of by means of an exchanger, as illustrated by Fig. 1, thus eliminating one heat transfer surface. This direct supply of well water in this manner is generally used on small systems, but may be used on larger systems, pro viding the well water is chemically acceptable and does not unduly contaminate the heat transfer surfaces. The operation of the air-to-liquid cycle shown for Fig. 2, is identical to that described for the well water system of Fig. 1, except that outdoor air infite&d of well water is the heat source and heat sink. Fig. 3 uses air as the beat source and heat sink, and as the heating and cooling medium, by changing the direction of the refrigerant flow. The use of direct-expansion type heat transfer surfaces in this manner will also provide either independent or simul taneous heating and cooling. Also, the heat removed from areas requiring cooling may be transferred to the zones need ing heating in a similar manner to that described for the in direct systems. One advantage of the direct type system is the elimination of the additional heat transfer surfaces. This advantage may be offset in some installations by.the pre cautions which must be observed to assure proper refrigerant flow and to obtain the desired capacity modulation. Each installation must be evaluated to determine which cycle is the most practicable and, at the same time, provides the most satisfactory performance. Such an analysis particularly ap plies to a multi-zone installation or to a system in which the heat source and heat sink equipment must be located a con siderable distance from the compressor. A further improvement in efficiency with a corresponding lower operating cost frequently can be achieved by incor porating a storage tank in the system, as illustrated by Fig. 4. A double-circuit condenser (two sets of tubes in a tingle shell) is used to avoid contaminating the heating circuit with dirt from the cooling tower circuit and, at the same time, to localize the cooling tower water treatment and to enable main taining independent water pressures in the two circuits. In this * To provide dmdtaneous heating and cooling by changing direchon of refrigerant Boer, Fig. 3 . .. Air-to-Air Heat Pump Cycle* cycle the excess heat from the internal zone (over that re quired by the exterior zone) may be stored in the tank for use as supplemental heat when the structure heat loss exceeds the internal heat gain. Storage tanka permit off-peak direct elec tric heating, as well as off-peak cooling during the summer period, in order to take full advantage of the lower electric energy rates available from many utilities. The operating cycle of the arrangement illustrated by Fig. 4 is similar to that described for Figs. L and 2, except that the excess heat from the structure either can be transferred to the storage tank, or rejected to the cooling tower. Generally, the modulating valve in the condenser circuit maintains a pre determined supply water temperature to the zone units. As the water temperature rises above this setting, the valve is positioned to divert the warm water to the top of the storage tank &nd to use the lower temperature make-up water from the bottom of the tank. When the excess heat from the struc- * To reclaim internal heat for heating of perimeter area and veatihtien dr. Heat refected from the system is stored m the tank far owe as orpptemeetd heat eheti shoctme heat loss exceeds the interned gain. Storage tank permits off-peak direct electric heating, as vrett os off-peak coding daring the tammer period. Fig. 4 .... Heat Pump Reclaiming Cyde* Heat Pump Systems for Air Conditioning 55 ture can no longer be transferred to the storage tank, the second condenser pump is operated and the excess heat is re jected to the cooling tower. During periods when more sup plemental heat is needed than that available from the internal area, the 3-way valve in the condenser circuit is positioned to use the wanner water from the storage tank. When the tem perature of the storage tank water is reduced below a level tbst is no longer applicable for direct heating, the 3-way modulating valve in the chiller circuit can be positioned to use the stored water as the heat source. A considerable quantity of additional heat can be recovered from the storage fpnk water by reducing its temperature to 40-45 F. The same operating cycle can be used to provide off-peak storage of cold water during the summer periods. EQUIPMENT SaECnON The heat source and heat sink surfaces, heating and cooling surfaces, compressors, and accessory equipment are sized and selected in -accordance with current refrigeration and airconditioning practices discussed in Chapters 28, 32, 33, 34, 36, 39, and 41 of the 1961 Guide And Data Book. The ca pacity of the system must meet both the design heating and -requirements. Normally, the refrigeration equipment is first selected to meet the cooling load and then checked with the beating load to see if the required temperature lift and balance can be obtained to operate successfully as a heating system (see Chapter 58 of the 1961 Guide And Data Book). Supplemental Heating The heating needs may exceed the capacity available from equipment selected for the cooling load, particularly if out door air is used as the heat source. When this condition occurs, consideration must be given to supplemental heating or to additional compressor capacity. The additional comprea- low Stage Redprocat'mg Rotary Centrifuged Redprocatmg High Stage Redprocatmg Reciprocating Centrifuged Centrifvgd Provides tera-stage compound coespretdoo for low outdoor air feet- 5 .... Air Source Heat Pump with Series-Parallel Compressor Arrangement* sor capacity, or the supplemental heat, is generally used only in the severest winter weather and, consequently, will have a low usage factor. Each of the two possibilities must be evalu ated to determine the most economical selection. Heating and Cooling Load Estimates Realistic winter outdoor design temperatures should be selected in order to obtain authentic heating requirements and to prevent installation of oversized supplemental heating equipment. The winter design temperatures given in Colump 6, Table 2, Chapter 25 in the 1961 Guide And Data Book, should be used unless experience and more authentic data for the par ticular locality are available. The experience of some utility companies has shown that values selected from Col. 7, Table 2, Chapter 25 of the 1961 Guide And Data Book, will give satisfactory results. The use of heavily conservative heating requirements and lowering the nightly indoor temperature are not recom mended, because the resulting additional heating capacity would unnecessarily increase both the first and operating costs of the system. Instead, consideration should be given to the use of operating cycles employing auxiliary equipment to provide higher operating efficiencies, and to all means of load reduction, including: 1. Employing the maximum, practical amount of insulation with proper vapor barrier in sidewalls, ceilings and floors of a structure. Windows and doors should at least be weatherstripped and properly caulked, and in most areas of the country storm windows and doors, or the equivalent, can be justified. 2. Utilization of available, dependable heat sources within the structures, such as lights, motors, heat producing machinery, and people. 3. Automatically closing the outdoor air intakes during nights, weekends and other unoccupied periods, so that the heat loss will be limited to transmission and infiltration. 4. Proper selection of the ventilation air. Because the ventila tion air load is an appreciable part of the total, reasonable ventila tion quantities, without sacrificing a healthful environment, should be selected. Minimum quantities of outdoor air may even be unacceptable, because of objectionable irritable and toxic odors in the atmosphere due to a high percentage of hydrogen sulfide, smog, and other chemical effluences from industrial processes. It has been found that physical and chemical odor removal units, such as activated charcoal in combination with a conventional or electric air filter, are effective in purifying and removing odor causing substances (see Chapter 10 in the 1961 Guide And Data Book, and Chapter 74 in this volume). The quantity of ventilation air can frequently be reduced considerably, resulting in savings in both first cost and operating cost. Reciprocating or Centrifugal Compressors Both the reciprocating and centrifugal types of compressors can be used for the central plant type of heat pump system. Present available experience does not permit an evaluation of the exact size for shifting from one type to the other. Most air source installations have employed single stage reciprocating compressors, but also the use of multistage' compressors has increased. The two-stage compound com pression system is particularly applicable in the extremely northern climate where the frequent occurrence of low out door temperatures makes the single stage system impracti cable. In the two-stage arrangement shown in Fig. 5, the compressors can be used in parallel during the cooling-cycle and in series during the heating cycle. The main advantage of staging is the resultant smaller heat-source, heat-sink surface (due to the larger possible air-refrigerant temperature dif ference) and the proportionally smaller auxiliaries needed to provide a given heating effect at the lower outdoor tempera tures. At an outdoor temperature of approximately 15-20 F, the performance of the two-stage and single stage systems is