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674 Chapter 38 '_________ . .. . 1945 Guide important enough to justify the omission of ventilation from certain . spaces which have only small heat gains and do not require fresh air for other purposes. The relation between supply and exhaust ventilation depends on the type of space, and the space's relation to the weather. In any case, it should be remembered that positive means for supply and exhaust must always be provided. Where natural ventilation is anticipated, infiltration and exfiltration via open doors, windows, etc., cannot always be con sidered adequate for this purpose. In addition to the ventilation requirements, but closely related to and usually forming an integral part of the study, is the manner in which heating shall be furnished for cold weather conditions. In all spaces which are provided with mechanical supply ventilation, where heat is also required, the simpler method and most economical from standpoint of weight is that in which duct type or blast heaters are fitted in the venti lating systems. Where this type of heating is furnished, convectors or radiators should be provided for spaces requiring heat but not furnished with mechanical supply ventilation. The most satisfactory arrangement for this method of heating, except where individual space control is essential, is zone heating. To accomplish this, the ventilation supply system, with the fan operating at slow speed (usually about 50 to 70 per cent delivery.) passes the air over a preheater which raises the air to a temperature of about 40 to 60 F. This preheated air is then passed . through the system and thence through one or more reheaters which are located in the ducts and so arranged that each serves a group of spaces which possess the same or similar heating requirements. It may be necessary to slightly revise the individual space air quantities, which have been determined on the basis of summer cooling, in order to bring them in line with the reheat or delivery temperature. In some cases central heating is used. By this arrangement all the air needed for heating is passed through the preheater and reheater fitted in series. This system has the disadvantage of affording poorer thermostatic control and cruder heating properties. In all installations of duct type heaters, however, care must be taken in the first stage of heating (preheater) to provide protection against freezing, either by heater design or compensating auto matic valve control. Of course, many of the usual. combinations or variations of duct type and convection or radiant heaters may be used with varying degrees of satisfaction, depending on basic design require ments such as weight and space limitations and economic justification for refinements. REQUIREMENT FOR VARIOUS TYPES OF SPACE In the paragraphs which follow the most important considerations are given for the treatment of the various spaces, but the resulting quantities of air should in all cases be checked with those shown in Table 1. Machinery Spaces The prime purpose of machinery space ventilation is to maintain a habitable temperature for the operating personnel. Of secondary impor tance is the necessity for preserving temperature conditions satisfactory for the successful operation of machinery, particularly of that designed . for certain maximum ambient temperatures. High dissipation of heat, from high temperature steam equipment or from high powered electrical installations, make it more practicable' to use spot cooling of working Marine Heating and Ventilation 675 Table 1. Typical Heating and Ventilation Practices for Ships Space Crews Quarters.-------Toilets and Showers.. Chart House________ Passenger & Officers Qtrs. Mess Rooms--:-------------- - Type of Ventilation Sup. Mech. Nat. Mech. Mech. Mech. Mfech. Exh. Mech. or Nat. Mech. Mech. or Nat. Mech. or. Nat. Mech. or Nat. Mech. Or Nat. Type of Heating H.B.a or D.Rh D.R. H.B. or D.K. H.B. or D.K. H.B. or D.K. H.B. or D.R. Air Change Minutes 5-6 3-4 5-6 4-6 . 5-6 4-6 J e t a Dining Salons-- Mech. Mech. or Nat. H.B.. or D.R. Galley and Pantry.... Mech. & Nat. Deck Pantries (No cook Mech. ing Equipment)--Stores Spaces (Adja . & Nat. Mech. to Living Quarters) Stores Spaces (Isol . or Nat. Mech. Locations)_________ _ or Nat. Hospital Spaces-..-- _ Mech. t LockersShops_____ ,, NatMech. Group Berthing Spaces... _ Mech. COj Bottle Space---------- .. Nat. Battery Room--------------- Nat. Laundry______ Mech. Mech. H.B. Mech. Nat. or Mech. Nat. or Mech. Mech. h.b: or D.R. ............ . __ ___ ___ H.B. or D.R. Mech. Mech. or Nat. Mech. or Nat. Mech. Mech. Mech. H.B. or D.R. H.B. or D.K. '________ D.R. H.B. ._ Mech. or Nat. Stearing Gear Space.------ ... Mech. or Nat. Dry Stores... ... Mech. Gyro Room.. ... Mech. Theaters and Halls.------------ Mech. Passageways- -. Nat. Nat. or Mech. Mech. or Nat. Nat. or Mech. Nat. or Mech. Nat. or Mech. Nat. H.B. or D.R. ___ _____ H.B. or D.R. D.R. Misc. Machinery.. Stair Wells.. ... Mech. Mech. or Nat. or Nat. __ Mech. Mech. or Nat. or Nat. ._. Nat. Mech. ... Nat. , Nat. ______ ;__ _____ D.R. i 3-6 e t 3 1-2 ' 3-6 15-20 15-30 4 15-20 6-10 3-6 10 2 1-4 Temperedair Sup. 20-30 2-6 Unit Heater if desired. 6-10 3-6 6-8 -- Exhausting or- Supplying ad jacent Quarters. 1-2 2-4 10 Same as pas sageways. Exh. at top. H. B.--Hot Blast System. *>D. R.--Direct Radiation.