Building Load and Energy Simulation
Review Topics for Test 2
-Derive the heat balance (conservation of energy) equation for the exterior or interior surface of a
building wall or roof.
-Explain the physical meaning of the various terms and factors in the heat balance boundary condition
equations.
-Sin() and Cos() significance in I sol and I sky components of heat balance surface equations.
-Range of values for I sol and approximate value for I sky.
I sky is a constant 21 BTU/hr/ft^2
I solar ranges from about 1 kW/sqm max
- Know the components of I sol
-Rationale, methods and results of linearizing radiation exchange between surfaces. Why linearization
not applicable or needed for I sol and I sky factors.
-Typical values for h convective and h rad for building load and energy simulation calculations.
-What physical parameters and conditions influence the magnitude of h convective and be able to explain
the physical meaning of the changes
-Meaning of h conductance and what assumption allows it to be employed to further simplify boundary
calculations.
-Derive the Sol – Air exterior surface boundary temperature and know the physical meaning of the
terms. Why is it used instead of the actual exterior surface boundary equation?
-Derive the Fourier heat condition PDE for thermal flow through a building and know what conditions
and parameters need to be known to solve by any method – analytical or numerical.
- Significance of thermal diffusivity properties in heat load calculations – peak load, timing of peak
load.
-Derive the Solar Heat Gain Factor [glz I sol +  glz*hi/(hi +ho)] and know physical meaning of terms
and relative importance of the two factors  glz I sol ,  glz*hi/(hi +ho)
-Full glazing heat gain equation which includes conduction through glazing between outside air and
inside air
-Heat gain vs space load in a zone and reasons for time lag differential
-Inverse Modeling Techniques (IMT) for a building or an energy using subsystem within a building
-Type of IMT models: 4PC, 3PC, 5 PC
-What is it?
-How is it done?
- Why is it done?
- Expected IMT models before and after an energy efficiency renovation
-Reasons for lack of predictive, forward models in building systems.
-Effect of part load operation on energy efficiency in building operation and difference between
reduced energy use and energy efficiency
- Relationship of part load operation and ASHRAE Design Day approach to equipment selection
- What properties would a building need to have to avoid the part load inefficiency syndrome?
- Be able to explain the greenhouse gas phenomena explanation for climate change.
Sun strikes the earth’s atmosphere.
The solar constant is the average amount of energy striking one square meter
(perpendicular to the suns’ rays) each second at the top of the earths’ atmosphere. The
satellite measured solar constant is 1366 W/m2.
Of this energy reaching the top of the atmosphere as much as 70% can be absorbed &
reflected by the atmosphere
Solar radiation enters the atmosphere and strikes earth’s surface
Solar insolation is the amount of energy received by the sun at the earths’ surface. On a
clear day ~1000 W/m2 (~317 BTU/hr- ft2)reaches a surface perpendicular to the
incoming radiation. This energy varies due to the angle of the incoming radiation and
again cloud cover.
Solar radiation that isn’t absorbed by the earth’s surface is reflected back into the
atmosphere towards space
Greenhouse gas molecules in the atmosphere absorb and re-emits some of the infrared
radiation BACK DOWN TO EARTH. This warms the earth’s surface and lower
atmosphere.