Document NEn4D8Ope4nYe2oG12NYXgoBD

American Society of Heating and Ventilating Engineers Guide, 1936 -a HEAT EQUIVALENT OF AIR ENTERING BY INFILTRATION The heat required to warm cold, outside air, which enters a room by infiltration, to the temperature of the room is given by the following equation: Hi = 0.24 Qd (/ -- t0) (3) where Hi = Btu per hour required for heating air leaking into building from outside temperature t0 to inside temperature t. Q = cubic feet of air entering per hour at inside temperature t. d -- density (pounds per cubic foot) of air at inside temperature t. t = inside temperature at the proper level. to = outside air temperature for which heating system is designed. 0.24 = specific heat of air. I It is sufficiently accurate to take d = 0.075 lb, in which case the equa tion reduces to Hi = 0.018 Q (t - to) (4) While a heating reserve must be provided to warm inleaking air on the windward side of a building, this does not necessarily mean that the heating plant must be provided with a reserve capacity, since the inleaking air, warmed at once by adequate heating surface in exposed rooms, will move transversely and upwardly through the building, thus relieving other radiators of a part of their load. The actual loss of heat of a building caused by infiltration is not to be confused with the necessity for-pro viding additional heating capacity for a given space. Infiltration is a disturbing factor in the heating of a building, and its maximum effect (maximum in the sense of an average of wind velocity peaks during the heating season above some reasonably chosen minimum) must t}e met by a properly distributed reserve of heating capacity, which reserve, how ever, is not in use at all places at the same time, nor in any one place at all times. REFERENCES Air Leakage, by Houghten and Schrader (A.S.H.V.E. Transactions, Vol. 30, 1924). Air Infiltration through Various Types of Brick Wall Construction, by Larson, Nelson and Braatz (A.S.H.V.E. Transactions, Vol. 35, 1929). 'n ' Infiltration through Plastered and Unplastered Brick Walls, by F. C. Houghten and Margaret Ingeia (A.S.H.V.E. Transactions, Vol. 33, 1927). Air Leakage around Window Openings, by C. C. Schrader (A.SlH.V.E. Transactions, Vol. 30, 1924). Effect of Frame Calking and Storm Sash on Infiltration around'and through Windows, by Richtmann and Braatz (A.S.H.V.E. Transactions, Vol. 34, 1928). Air Leakage on Metal Windows in a Modem Office Building, by Houghten and O'Connell (A.S.H.V.E. Transactions, Vol. 34, 1928). " The Weathertightness of Rolled Section Steel Windows, by Emswiler and Randall (A.S.H.V.E. Trans actions, Vol. 34, 1928). Air Leakage through a Pivoted Metal Window, by Houghten and O'Connell (A.S.H.V.E. Transactions, Vol. 34, 1928). Pressure Difference across Windows in Relation to Wind Velocity, by Emswiler and Randall (A.S.H.V.E. Transactions, Vol. 36, 1930). Air Infiltration Through Various Types of Wood Frame Construction, by Larson, Nelson and Braatz (A.S.H.V.E. Transactions, Voli 36, 1930). Neutral Zone in Ventilating, by J. E. Emswiler (A.S.H.V.E. Transactions, Vol. 32,1926).. Air Infiltration Through Double-Hung Wood Windows, by Larson, Nelson and kubasta (A.S.H.V.E.' Transactions, Vol. 37, 1931). m 140 3 Chapter 6--Air Leakage T 11 Buildings, by H. L. Alt (.Healing. Piping and Air Conditioning, May. 1932). AFliureInAfcilttiroandoinnTahrougt.^steel Framed Windows, 1932). by D. O. Rusk, V. H. Cherry and L. Boelter (.Healing. PipiInngveasntidgaAtitorn of An rO>u,.Htleettss imn Class Room Ventilation, by Larson, Nelson, and Kubasta (A.S.H.V.E. Transactions. ' Influence of StacK c-uc'- the Heat LoS3 in Tall Buildings, by Axel Marin (A.S.H.V.E. Transactions, Vol- 40, 1934). Wind Veloo^es and Carl Gutter Rnildine and Their Effect on Heat Loss, by F. C. Houghten, J. L. Blackshaw, ^ TANSACTlONSt Vol. 40, 1934). PROBLEMS IN PRACTICE Wh is it important in exterior walls of air space construction to place a d stop in the outer surface? n ' tr the heating season, air within the space is at a higher temperature than outdoor n'ifTracks are present in the outer surface, a chimney action takes place which causes air' tinuous change of air in the space. This causes a greater heat loss through the ? wan surface for two reasons: (1) the temperature difference becomes greater and (2) the surface coefficient on the air space side is increased because of the higher air velocity Another undesirable condition resulting from this leakage is a lowered temrature of the inside surface. The increased radiation from occupants to walls caused bythis condition must be offset by higher air temperatures. The wind stop in the outer wall surface is therefore important because: a. It reduces the loss of heat through the wall. 2 Why is it essential to consider this in heating calculations? The inflowing air displaces inside heated air and must be heated up to the internal temperature. S Where is it necessary to consider infiltration created by temperature difference? In tall, single-story buildings and in multi-story buildings where the floors are not adequately isolated. 4 Why is the infiltration in a building less than that determined in laboratory tests? In laboratory tests, the indicated wind velocity is measured by the difference in pressure on the two sides of a single wall, window, or object tested. In a building, an internal back pressure is built up between its walls to a point where outflow on the lee side is equal to inflow on the windward side and this back pressure reduces the actual inflow below that determined in the laboratory for a comparable wind. 5 Is heat loss by infiltration through walls of importance? Only in the case of simple walls or poorly constructed compound walls. 6 What measurements are required to calculate the heat loss through doublehung wood windows? Sash crack (equal to the sash perimeter plus the meeting rail) and frame crack (equal to the frame perimeter). 1 What is the basis for selecting the wind velocity and outside temperature to be used in making infiltration calculations? Weather Bureau records. The wind velocity taken is the average during the three coldest months and the temperature used is the lowest on record for the given locality. 141