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T a b le 29. R ate of H e a t G a in F rom A ppliances W ITHOUT HOODS" (Concluded) H a ir D ryer. Blower Type H a ir D ryer, H elm et T y p e , Perm anent W ave M achine Neon Sign, per linear f t o f tube Steriliser, Instrum ent 1 Burners, Laboratory Sm all Bunsen Sm all Bunsen F is h ta il F is h ta il Large Bunsen C igar Lighter j H a ir D ryer. 5 helm ets Stoves. Oven 306 Oo uX i<Sg* OUocDHa uz H "OMa' <W s*<5fe'Sg- CHAPTER 12 2700 160 8 8 oo * 2 88 8 . 00 -8 8 co 1200 2300 1870 ;*88 1952 Guide 9200 ; 2300 j 11500 1800 1 9000 1 1000 4000 - 19000 oOCS oO-oiOoOfOlOoC-J > ooooo: vreo O o 1 S' .- ooCOooCOooCOoo00no>o o nf-nn 15000 6000 8500 * 7200 1 | 25000 25000 1 2500 | 33000 Pan, 165 w ; Low, 915 w ; H igh, 1580 w Fan, 80 w ; Low, 300 w ; H igh, 710 w ' 60 heaters a t 25 w each, 36 in norm al use ; F o r physicians: therm o stat cuts off 550 w 1100 , before boiling 5400 2400 3750 a A gO o 8 oNto- 8 *Q ' 0009 Q 1 -m z 3H 8 S5 S SdBd at at *0*0 5 3 Po Po ii oil pi S!1 An 2 3 Sg o-JaSgSiZ2 d"3|S <SXQg igsog|s"K On "Ag' 222 .< M anufactured Gas N atural Gas M anufactured Gas , N atural Gas ' A djustable orifice | C ontinuous Flam e | H eater and fan blow ing a ir to helmets Insulated, modern N o t Insulated 8888 Q*-O<cOoOcoU*3oo 22222 2 < :i?l!| ed fl a Si CQEQttmS 333.23 SSSSx sa ea s A& - AI3 s3 3.3 8S jjs 5=3 a! .s2*sa) .w ,fr 1? *52 3*0 *53 |8 3 f nS 38 i U<C3 ace9. j fi S SSr8S Cooling Load 307 the conditioned space. If the motor is without the space, then do not divide by the motor efficiency in Equation 16. The load factor is merely the fraction of the rated load which is being delivered under the conditions of the cooling-load estimate. Motor efficiencies may be approximated as follows: about 50 to 60 percent at $ hp rating, increasing to 80 percent at 1 hp, and to 88 percent at 10 hp and above. Appliances. Care must be taken in a cooling-load estimate to take into account the heat gain from all appliances, electrical, gas, or steam. Table 29 presents, recommended data.28 Note that the maintaining rate in Table 29 is the heat input required to maintain the appliance at the normal operating temperature even though it is not being used, i.e., no coffee is being made, no toast is being made, no food is being cooked in the fry kettle, etc. The maintaining rate is useful in setting up a lower limit to the heat gain to a room from the appliance when in operation. Experienced judgment must be used in the application of data given in Table 29. Consideration must be given to the heat contributed by appli ances which are in use at the time of peak load-. The quantity of heat will depend upon whether products of combustion are vented to a flue, whether they escape into the space to be conditioned, or whether appliances are' hooded allowing part of the heat to escape through a stack. There are no generally accepted data available on the effects of venting and shielding heating appliances, but it is believed that when they are properly hooded with a positive fan exhaust system through the hood, 50 percent of the heat will be carried away and 50 percent dissipated in the space to be con ditioned. The same effectiveness of the hood should be figured for both latent and sensible heat. LOAD FROM MOISTURE TRANSFER THROUGH PERMEABLE BUILDING MATERIALS The diffusion of moisture through all common building materials is a natural phenomenon which is always present to a greater or lesser degree. The permeability values for various building materials are given in Table 22 of Chapter 9, together with an explanation of moisture transmission through these materials. In the usual comfort air-conditioning application, it is common practice to neglect moisture transfer through walls, for the actual rate is quite small and the corresponding latent-heat load is hardly significant. So-called vapor barriers are frequently employed in modern construction for the pur pose of keeping moisture transfer to a minimum, and reducing the de teriorating and insulation-destroying effects of moisture. Industrial jobs, on the other hand, frequently call for a low moisture content to be maintained in a conditioned space. Here the matter of moisture transfer cannot be neglected; indeed, it is quite possible to have the latent-heat load accompanying this transfer be of greater magnitude than any other latent-heat load. The equation for computing this load is: M / Vapor Pressure \ 7000 \Difference, In. Hg/ * 1076, Btu per (hr) (sq ft) (17) where it = permeability grains per (sq ft) (hr) (in. Hg). 7000 = grains per pound.