Builduing Energy Use
Buildings account for about this percentage of US energy consumption
28%
A large office building requires cooling even when outdoor temperatures are 55°F because of this type of heat gain.
internal load
P x t =
E
three mechanisms of heat transfer
conduction convection and radiation
uncontrolled air leakage throug hcracks in buikldiungs
infiltration
US uses about this % of the world's energy
17%
This type of building experiences heating loads that are strongly influenced by outdoor temperature because internal heat gains are small.
envelope dominated buildings
A device rated at 1500 W operates for 3 hours. The total energy consumed is this many kWh.
1500 W = 1.5 kW
1.5 × 3 = 4.5
→ What is 4.5 kWh?
define coduction, convection, radiation
solids/touching, moving air / fluids / electromagnetic waves
airmovement caused by warm air rising in =side a buiklding
stack effect
This metric measues energy used per squsre foot per year
Energy Use Intensity (EUI)
If lighting, equipment, and occupants provide enough heat to offset envelope losses, the outdoor temperature at which heating is no longer required is called this.
balance point temperature
If electricity costs $0.20/kWh and a 2 kW heater runs for 5 hours, the cost of operation is this.
2 x 5 = 10 kWh
10 x 0.20 = $2.00
Radiant heat transfer between two surfaces depends strongly on this geometric requirement.
line-of-sight exposure etween surafces
wind creates positive pfessure on te windward side and this pressure on the leeward side.
negative pressure
units for EUI are...
kBtu / ft^2 / yesr
Compared to residential buildings, commercial buildings typically have a lower balance point temperature because of this factor.
higher internal heat gains
The unit Btuh represents energy per unit time and therefore measures this physical quantity.
what is power?
A building with extremely high internal loads may require cooling even during winter.
Internal heat gains from lighting, equipment, and occupants exceed envelope heat losses, causing the building to overheat.
heat loss equaion through uilding materials
q = U x A x deltaT
this term describes buildings where internal heat gains dominate energy balance.
internally dominated buildings
Why do internally dominated buildings typically have lower balance point temperatures than residential buildings?
Because internal heat gains provide additional heating, reducing the outdoor temperature at which heating is required.
A building consumes 50,000 kBtu annually and has an area of 10,000 ft². Its EUI equals this.
50,000 / 10,000
→ What is 5 kBtu/ft²/year?
Two buildings have identical floor area. One is compact and tall, while the other is spread out with many exterior walls.
Which building will experience higher envelope heat losses?
The spread-out building because it has a higher surface area-to-volume ratio.
heat loss equation caused by ventilation air flow
q = 1.08 x CFM x deltaT