Heat Transmission HVAC CNST 305 Environmental Systems 1 Dr. Berryman

Temperature Gradients The temperature differential between two separate surfaces as heat transmits across them. A Proportional calculation Uses IA OA Temperatures R values Purpose Determine surface temperatures MRT Dew Point

Develop Thermal Resistant Values AL Siding ¼” USB R19 Batt 3/8” Gyp Board IA Air Film OA Air Film 21.37R TOTAL = R values Wall Section Note: This is an actual construction in Grand Island

Determine Design Temperatures (winter) AL Siding ¼” USB R19 Batt 3/8” Gyp Board IA Air Film OA Air Film R TOTAL = R values Lincoln, NE OA –5 o F IA 75 o F t = 80 o F

Calculate Gradients Lincoln, NE OA –5 o F IA 75 o F t = 80 o F OA Air film: 80 o F x = 0.6 o F = AL Siding: 80 o F x2.3 o F =80 o F x 71.1 o F R19 Batt: AL Siding ¼” OSB R19 Batt 3/8” Gyp Bd IA Air Film OA Air Film R TOTAL = R values And so forth… [ t x R R TOTAL ]

Surface Temperatures Lincoln, NE OA –5 o F t = 80 o F IA 75 o F AL Siding ¼” OSB R19 Batt 3/8” Gyp Bd IA Air Film OA Air Film o F o F o F o F o F o F o F R TOTAL = R valuesGradients H C Gypsum Board Room Side Surface: 75 o F – 2.3 = 72.7 o F [ t x R SUM R TOTAL ] IA -

Surface Temps (cont.) Lincoln, NE OA –5 o F t = 80 o F AL Siding ¼” OSB R19 Batt 3/8” Gyp Bd IA Air Film OA Air Film o F o F o F o F o F o F o F R TOTAL = R valuesGradients H C Gypsum Board Wall Cavity Surface: 75 o F – ( ) = 71.5 o F IA 75 o F

Surface Temps (cont.) Lincoln, NE OA –5 o F t = 80 o F AL Siding ¼” OSB R19 Batt 3/8” Gyp Bd IA Air Film OA Air Film o F o F o F o F o F o F o F R TOTAL = R valuesGradients OSB Board Cavity Surface: 75 o F–( )= 0.4 o F IA 75 o F

Heat Transmission -20 o 10 o 0 o -10 o 20 o 30 o 40 o 50 o 60 o 70 o 80 o F Temperature Lincoln, NE OA –5 o F IA 75 o F AL Siding ¼” OSB R19 Batt 3/8” Gyp Bd IA Air Film OA Air Film o F o F o F o F o F o F o F R TOTAL = R valuesGradients H C OSB Cav Side 0.4 o F Gyp Cav Side 71.5 o F OSB OA Side -2.1 o F Siding Surface -4.4 o F Gyp Rm Side 72.7 o F

Application? Case Study Scenario: You have been called in as a consultant to find out why a certain building is having the following problems: On the south side of the building, the sheathing is warping between studs Same side…AL siding is popping loose During the winter they occupants cannot keep the building any warmer than 65oF (in fact, some liquid items near the north facing wall have froze) Also, at different point of time in the winter, all of the insulated double pane glass has frosted over on the inside Snow has accumulated on the inside during heavy blustery snow storms High electric bills for heating and cooling

At inspection, you see… North Side Siding warps Siding pulled away

You see… South Side Siding warps in and out every 16”

You see… North Side Windows You note that the snow extends into the closet

Wall inspection Nothing behind AL siding but bare OSB sheathing R19 batt insulation not properly installed mmhhh….. Request Blower Door Test

Blower Door Test A blower door is a large calibrated fan that is temporarily mounted in a house door to measure the "leakiness" of the house Smoke puffer Infrared camera Calculate room air change A recreation of a 20 mph wind

You discover… Air leaks Around doors and windows Behind plumbing fixtures Between sill plate and floor Infrared Shows air infiltrating around each insulation batt and at sill plate Calculations from pressure differentials 133 CFM infiltration (ASHRAE recommends 10 cfm for residential) 35 CFM ventilation

Your Notes after Inspection Heating/Cooling sized correctly You sketch the wall construction Determine R values Wall Window IA conditions: DB=75 o F WB = 56 o F Calculation winter surface wall temps

What next?

Check for condensation w/in walls -20 o 10 o 0 o -10 o 20 o 30 o 40 o 50 o 60 o 70 o 80 o F Temperature Heat Transmission and Exfiltration (ventilation) Infiltration IA: DB=75 o F WB = 56 o F OA: DB=-5 o F DP: 39 o F

DS Glass Air Space DS Glass IA Air Film OA Air Film R TOTAL = R values Lincoln, NE OA: –5 o F t = 80 o F IA: DB=75 o F WB = 56 o F Check Windows Inside Surface Temperature? 48 o F W/30% RH DP=39 o F What about 40% or 50% RH

Next Time Heat Gains Chapter 2.6 – 2.8 (Toa)rooflights equipme nt floor exteriorwall glass solar glass conductio n infiltration people