Document DDLvVdvy6ZJgoaX14Ozz6K9E4

HEATING VENTILATING AIR CONDITIONING GUIDE 1943 of the float regulator, or by properly charging the plant in the case;of the high pressure float drainer. The thermal expansion valve system depends' upon the thermal valve automatically feeding just as much liquid to the coils as is required to maintain ..the superheat at the coil suction outlet within predetermined limits which vary from about 6 to 10 F. The CHAPTER 26. HEAT TRANSFER SURFACE COILS coil must be so arranged that the required suction superheat can be attained with a minimum sacrifice, in the performance of the coil. as . a-, whole. It is. general practice to attain this superheat within ,the coil itself and not by the use of external heat exchangers or other auxiliary devices.. With thermal expansion valves it is advantageous to keep the pressuredrop through the refrigerant feeds as low as possible. The feeds are laid out to expose each to the same mean temperature difference so that ithandles the same refrigerating load. A distributing means is imposed between valve and coil liquid inlets to divide the refrigerant equally' among the feeds.- Such a distributor shall be effective for distributing both liquid and vapor, since the entering refrigerant is a mixture of the Fig. 3. Direct-Expansion Coil with Flooded System - Fig. 4. Direct-Expansion Coil with Thermal Valve System thermal valve arrangement is in common use for the type of coils covered by this chapter, while the flooded systefn is comparatively rare. With the flooded system the refrigerant distribution through the tubes depends on properly selecting the length, of the feeds and the head of liquid imposed upon the liquid inlets. No auxiliary distributing devices Fig. 5.' Types of Refrigerant Feed Distributing Heads are required. With the thermal valve system.there are two factors to> consider. There must, be, generally,, more than one refrigerant feed, through the coil per thermal,valve to keep the pressure drop through the refrigerant circuit within practical limits:and to reduce.the corresponding penalty in increased evaporating temperature: At the same time the 508 ' Fig. 6. Arrangement for . Face Control Fig. 7. - Arrangement'for :Depth Control- two. Fig. 5 shows three typical types oi distributors. In distributor.- A: the liquid and gas mixture from the thermal valve is led tangentially into a chamber. The coil feed connections extend outward radially at the top. of this chamber. In distributor B the refrigerant is discharged-at a high velocity through a central jet against the end plate, forming a uniform mixture of gas and liquid within the distributor, from which individual connections are led as shown. In type C the refrigerant enters at. high velocity from the thermal valve and is discharged against the end plug in which the individual liquid feeds are closely arranged. These distribu tors can be used in either vertical or horizontal position. Although there are other forms of distributors the ones mentioned are typical examples.: The individual liquid connections from the distributor to the coil inlet are; commonly made of'small.diameter tubing and are all of the same length- 509