You conduct an energy assessment for a newly constructed house during a hot summ
ID: 1767000 • Letter: Y
Question
You conduct an energy assessment for a newly constructed house during a hot summer day. The homeowners are very curious if their house is energy-efficient and what they can do to improve the current conditions. Considering the following inspection notes you have, suggest several cost- effective ways that can improve the house energy consumption. . ACHso value is 7.9 IR images indicate large temperature gradients around the main door, garage door, and several windows. You realized one of the bedroom ceilings that is exposed to the attic is considerably warmer than the others Page 2 of 2Explanation / Answer
-ACH50 stands for AIR CHANGES PER HOUR. It measures the number of times volume of air changes per hour at 50 pascal pressure. This number indicates about a building that how much it is leaky or air air sealed. To calculate the ACH50 value, we should have the CFM50 number.
To get the CFM50 number we need to run a door blower test in house. In this test, all the doors and windows closed. A powerfull exhaust blower fitted to a door to throw air from inside of a house to atmosphere. While doing so, the objective is to maintain -50 pascal pressure inside the house. Then we calculate the amount of air exhausted cubic per feet to maintain this -50 pascal inside the house. High value of CFM50 signifies that building is leaked. But sometimes this is not useful when comparing different structure buildings like large house and a small one. So we use ACH50 number also to make it more useful. To calculate ACH50 number, we multiply CFM50 number by 60 minutes per hour to find how much cubic feet per hour being exhausted from the house to maintain -50 pascal pressure. ACH50 represents the number of times to run exhaust per hour to maintain -50 pascal where as CFM50 represents the volume of air which should be exhasuted to maintain -50 pascal.
-IR images indicates large temperature gradient at main door and around windows. Large temperature gradient means difference between the outside and inside temperature. If it is large, it means high rate of flow heat from outside atmosphere to towards the gate and windows. To minimize the flow of heat, the thickness of glass and wood which are used to make doors and window need to be increased.
Q=-kAdtdx
Q= Rate of flow of heat (W)
k= thermal conductivity of body material (W·m1·K1)
A= cross-sectional area normal to direction of heat flow (m2)
dT/dx= is the temperature gradient (K·m1)
-Bedroom ceiling which is exposed to attic is warmer than the others may be due to ventilation problem. This problem can be solved by providing vents such as ridge or gable vent.
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