Energy and the Building Shell Flashcards
What’s the main difference between balloon and platform framing?
In balloon framing, the wall studs run from the ground floor to the rafters. In platform framing, the studs end at each level and new ones are built on top.
What percent of US homes are mobile homes?
6%
How wide is a single-wide and double-wide mobile home?
single: 10-16 ft.
double: 24-28 ft.
length: 60-80 ft.
What are some weaknesses of mobile homes?
Joints and holes in the HVAC system, torn or missing underbelly, the seam between a double-wide, plumbing penetrations
What are some points of weakness in multifamily buildings?
Thermal bridging at steel and aluminum, protruding doors, windows, balconies, roof penetrations, air intake and exhaust vents
What are the five ways heat flows in a building?
Transmission, air leakage, ventilation, solar heat, internal heat sources
What is Transmission?
The flow of heat through the building shell itself, driven by conduction, convection, and radiation.
What is air leakage?
Heat carried by air moving around the building shell via holes and other paths
What is ventilation?
Controlled air exchange between in and out
What represents the largest energy demand?
Heat loss and heat gain through the thermal boundary
What is K-value (k)?
The thermal conductivity of a material: how many BTUs flow through a 1 inch thick by 1 square foot piece of material at a temp difference of 1 degree F.
What material has the highest K-value?
aluminum
What is thermal bridging?
Heat flowing rapidly through conductive materials in contact
What is a thermal break?
Inserting insulating materials between high-conductive materials, common in windows and doors
What is U-factor?
The thermal conductance of a building material of a given thickness. Lower is better. Used to calculate heating and cooling loads.
What is R-value?
A measure of thermal resistance of building materials, or the ability to slow down conductive heat flow. Inverse of U-factor. Higher is better.
What is framing factor?
The percentage of an assembly that is made up of studs, and therefore does not contain cavity insulation.
The lower the framing factor, the _______ overall R-value.
higher
What is the US average framing factor?
25%
How do you calculate the overall average R-value of a wall assembly?
- Add up all R-values through the framing portion, change to U-factor.
- Add up T-values through insulation portion, change to U-factor.
- Multiply framing U-factor by framing factor. Multiply insulation U-factor by remainder of wall percentage. Add together to get overall U-factor.
- Convert overall U-factor to overall R-value.
What is Heating load?
The amount of BTUs per hour that need to be added into a house by mechanical means to maintain comfort, based on winter design conditions.
Heating load includes:
Transmission load (conduction) + Air exchange load (leakage and ventilation)
What is transmission heating load?
The BTUs per hour that flow through the thermal boundary by conduction.
Transmission heating load (BTUH) =
U x A x deltaT
U = overall U-factor
A = area in sq ft
T = desired indoor temp (70) minus winter design temp
