In November, 1968 a report was made to TC 2.5 (Fenestration) covering research conducted under RP69-Effect of Inner Surface Air Velocity and Temperature Upon Heat Gain and Loss Through Building Fenestrations. That study was limited to single glass types, and single glass with drapes or venetian blind shading, and the results were reported to the Society in Technical Paper No. 2156 in July, 1970.1 Bxiefly stated, the study showed significant increase both in heat gains and heat losses when supply air sweeps the interior glass surface. In view of those findings, TC 2.5 recommended a further study to determine the effect if insulating rather than single glass were used in the fenestration. Such a study was authorized as RP 104, was started October 1, 1969, and is reported here.

Three types of insulating glass were used in the cooling load (heat gain) analysis and testing: (1) double clear, consisting of a 1/4 in. panel of clear plate, a 1/2 in. air space, and a second 1/4 in. clear plate panel; (2) heat absorbing and clear, consisting of a 1/4 in. panel of heat absorbing glass on the outdo.or side, a 1/2 in. air space, and a 1/4 in. clear plate panel on the indoor side; (3) reflective and clear, consisting of a 1/4 in. panel of reflective glass on the outdoor side, a 1/2 in. air space, and a 1/4 in. dear . plate panel on the indoor side.

Each type was analyzed and tested without indoor shading (Fig. 1), with indoor shading consisting of a lightcolored venetian blind, and with indoor shading consisting of a medium drape (Fig. 2). Only types (1) and (3) were used in the heating load (heat loss) studies, the theory being that heat losses through the first two types would be essentially the same, since their "U" values under standard conditions are essentially the same.