Document kmMkbwaR16E2RnOLNwoEqbMVJ

H eat P omp H e a t Sources A nd Sin ks 810 s s <8 8 HI* < S B S' < 8H < . ao < d: 00 at . < H eat Source - Cit y Water Well Water .' Earth. Source Classification P rim ary S u ita b ility as Heat Good S in k A v a ila b ility Universal (Location) A v a ila b ility Continuous. * (T im e ) Expense (O riginal) Low,, less than earth and water sources ex cept city Expense (Operating) ' R elatively low Primary or auxiliary Good Cities C o n tin u o u s -^x c e p t local shortages U sually lowest High, usually prohibi tiveUeually satisfactory Variable w ith loca tio n (10 to 25 F Deg) Usually adequate Moderate Excellent A ir, earth 8cale'on coils. Local use restrictions d u r ing shortages. D is posal. Water tern-, perature m ay be come too low to per m it further heat ro. moval. P rim a ry Good Prim ary . Good ' P rim a ry Variable or auxiliary w ith source Prim ary or ,auxiliary ^ A uxiliary Usually poor None / Uncertain Ibtre Lim ited . , ' Extensive ' Universal C o n tin u o u s -- unless well runs d ry ' Continuous Variable Continuous, tempera- In te rm itte n t. . ture level drops Unpredietable, - from a m axim um to` a minimum.as heat except over * extended is removed,- slow ly- i. itim e .rises when pum p is 7 High, result of drilling Low j Variable inoperative H igh, usually lees than Unexplored the cost of d rillin g a w e ll :v well Low to moderate R elatively low' R elatively low Relatively moderate Unexplored. P ro m isin g , as'' auxiliary for reducing oper T e m p e ra tu re (Level) T e m p e ra tu re (Variation) Design In fo rm a tio n Favorable 75-95% of tim e in most of U. S. ' E x tre m e Inadequate Satisfactory Satisfactory U sually good ating coat In itia lly good-rdrops Excellent CHAPTER 36 w ith tim e and rate of heat withdrawal Small U sually adequate Moderate U sually ade' quate U sually moderate Large--lees than for air, however Adequate if source is Inadequate . Extreme . Practically available oonstant in supply and temperature Sue of Equipment A daptability to SoMuarscsesPirto duction may Augment 8 p e c ia lP ro b le m e Particularly bulky Excellent, can be factory assembled and tested Least heat available when demand great est. Coils m ay become frosted requiring extra capacity, alternate source, or standby heat. May require d u ct work. -Variable a ir tem perature makes control difficult. Moderate (except well) Moderate Variable (usually moderate) Moderate (except ground coils) Probably b u lk y Excellent, (except well) Excellent Poor Fair / / A ir, water A ir, earth, water Corrosion*, scale may form on heat trans fer surface. Disposal. Water location, tem perature, composi tion usually un kn o w n .u n til well Water may cause - scale, oorro- sion.and algae fouling. U sually scale form ing or L im ite d by local gool- . corrosive. O ften in- 1 ogy and climate. I n sufficiontsupply. Very stallation costs d iffi lim ited application, c u lt to estimate. Re Probably w ill require heat storage equip* raent at either `evaporator or oondenser side. henoe requires in d i quires considerable vidual design. ' ground area, may damage lawns, gar d rille d . Well m ay ' run dry. dens. 1952 Guide w Refrigeration 811 installing a smaller refrigeration plant, augmented by a storage system, and by operating it for longer periods. The Heat Pump It has been almost 100 years since Prof. William Thomson (Lord Kelvin) first proposed the use of a compressor'as a "warming engine" and as a means of heating buildings to replace equipment for direct burning of fuels. Several early working models were constructed, but the device has remained essen tially of laboratory interest until the last 20 years. Although frequently referred to incorrectly as the reverse cycle system, the heat pump cycle is identical with the ordinary refrigeration cycle, and differs only in the sense that the desired effect is rejection of the heat from the condenser rather than absorption of heat in the evaporator. A discus sion of the coefficient of performance for the heat pump is found earlier in this chapter. The first actual residential heat pump installation was probably made in Scotland in 1927 and since that time, a number of commercial and residen tial systems have been made in this country. Both progress and. growth of interest have been particularly rapid during the past four years and, consequently, at the present time there are several hundred residential in stallations and probably a greater number of commercial systems. . How ever much research is needed before the residential heat pump installation can successfully emerge to compete economically and wifi equal reliability with the more common forms of heating and fuels. - From an analysis of the equation for the coefficient of performance, it is evident that the economical adaption of the heat pump as a practical means of heating, requires that the temperature of the source from which the heat is extracted be as high as possible, and that the temperature of the sink to which the heat is rejected for heating purposes, be as low as possible. Thus, with a small temperature spread between the evaporator .arid the con denser, six or more times as much heat may be obtained theoretically (and three to five times practically) as the heat equivalent of the work necessary to operate the system. There are a number of limitations, however, the most serious of which is the lack of ready availability of a practical source of heat. One of the major problems in the development of the heat pump involves research on, and the compilation of reliable design data for, the various heat sources and sinks available. The four principal potential sources of heat are air, water, earth, and solar energy. Of these, the first three are primary sources of heat which may be used alone. The fourth, solar energy, while of tremendous potentiality, will probably be developed in most localities as auxiliary to the other three. In addition, there are other minor sources such as process waste heat, sewage, etc., which may be used under special circumstance. There are also a number of industrial applications of heat pumps, for purposes other than space heating, which are practical largely through economic considerations of the particular process involved. Table 4 pre sents a summary of the advantages and disadvantages of each of these major heat sources. By reference to Table 4, it will be seen that, to date, the most satisfactory heat sources are air, water, and earth, and that air and water are the most satisfactory heat sinks. There are, therefore, six possible combinations of source and sink in application: air to air, air to water, water to air, water to water, earth to air, and earth to water. In addition, it should be recog- IL*