MEEB - heat flow
How many air changes per hour does a typ building have?
.25 air changes per hour
What is the SHGC values for real products?
.9 to .2
One low E coating is almost as effective as what?
Adding another layer of glass.
What is convection highly dependent upon?
Air Motion
What must the aluminum foil face if it is to be as effective as a radiant barrier?
An air space
Where does the vapor barrier need to be installed?
As close to the warm side as possible. Typically just behind the interior surface.
Closed shell with punched holes
Barrier dominated
What are some examples of flexible and semi rigid insulation?
Batt and blankets
Convection is heat exchanged between what and what?
Between a fluid - typically air - and a solid
It is possible to measure the actual infiltration performance of a constructed building using a device called a what?
Blower door. Some energy codes require the blower door test.
How is U factor calculated?
By finding the resistance of each part including air film and air spaces and then adding these resistance to obtain a total resistance. The U factor is the receptacle of the Sum of these resistances.
What is heat flow through basement walls and floors complicated by?
By increasing length of heat flow path with increasing depth. Also the temperature of the earth is not equal to the ambient air temperature and becomes more and more out of phase with air temperature at increasing depths.
What are the two ways outdoor air can enter the building?
By means of infiltration and or ventilation.
How do you calculate infiltration through cracks
Calculate the length of the crack on the Windward exposure and multiply this by the respective air assembly leakage rate
The insulation value provided by layers of air is often listed as what?
Conductance, the reciprocal of resistance.
Open frame with building skin selectively added
Connector dominated
At the exposed surface of solids heat transfer takes place by what two ways?
Convection and radiation.
What are the three principal ways to lose or gain heat?
Convection, conduction, radiation.
What are infiltration and ventilation air flowrates expressed in?
Cubic feet per minute or liters per second
What do you some of the most effective insulating materials combined?
Dead airspace and layers of reflective film
Thermal capacity for material is obtained by taking the product of what two things?
Density and specific heat
The more absorbent material the higher the what
Emittance
What refers to power usage overtime?
Energy.
What are some examples of formed in place insulation?
Expended pellets or liquid fiber mixtures that are poured Frost, sprayed, or blown in place.
If two spaces have two different moisture contents where does the moisture flow?
From the area of greater concentration to the area of lesser concentration.
Went two objects are at two different temperatures heat flows from what to what?
From the hotter to the colder.
How does heat flow in radiation?
Heat flows via electromagnetic waves from hotter surfaces to detached colder ones
What does F2 stand for in the heat lost formula?
Heat loss coefficient for the floor slab/installation configuration
What does F stand for in the heat loss formula?
Heat loss coefficient for the wall/floor/installation configuration a given depth below grade
What is of greater concern under dynamic conditions rather than static conditions?
Heat storage within a material.
What type of SHGC is desirable for solar heating applications?
High
Three common types of low E coatings or what?
High transmission low E Selective transmission Low e (winter heating and summer cooling) Low transmission low E (use to shield the sun)
When are radiant barrier's useful?
In east and west facing wall's in warmer climates Also in roofs in warm climates.
When would you need to convert SHGC to SC?
In order to determine the overall shading performance of the glazing unit with external or internal sheeting devices.
What is cooling load equal to?
Instantaneous heat gain minus any part of that heat gain that is stored with in the building plus any previously stored gains that are now affecting air temperature.
What are some examples of loose fill insulation?
Insulating cement, a loose material mixed with the binder and traveled into place.
Where do you find the energy code for residential buildings?
International energy conservation code or model energy code
Which takes less energy to raise the temperature of? A low specific heat material or a high specific heat material?
It takes less energy to raise the heat of a low specific heat material
Filling an enclosed airspace with what has thermal benefits?
Krypton or argon
What type of SHGC is better for windows where cooling is the dominant thermal issue?
Lower
What is the uniform temperature of the surrounding enclosure in which radiant transfer from the human body would equal the actual radiant heat transfer within the building space?
Mean radient temperature
Is thermal bridging more serious in metal studs or wood studs?
Metal studs.
Latent heat flow result in a change in what
Moisture content. Often humidity of the air.
What is the principal means of latent heat loss or gain?
Moisture flow through envelope assemblies and via air leakage.
How many air changes per hour does a leaky building have
One air change per hour
What are the two concepts that can illustrate a fundamental range of choices surrounding envelope intent?
Open frame and closed shell
What does V stand for in the heat loss formula?
Outdoor air flow rate in CFM
What does P stand for in the heat loss formula?
Perimeter of the floor slab.
The what of the material of construction is the latent equivalent of sensible conduction?
Permeance
What refers to the instantaneous flow of energy at any given time?
Power
What can thermal capacity do to heat flow the storage?
Reduce heat flow.
What is an important added benefit of low E glazing?
Reduction of UV transmission thus reducing fading of objects in room.
ASHRAE Comfort zones are primarily defined by what?
Relative humidity and dry bulb temperatures
In the winter it is not unusual to add water vapor to the air in the building to keep the what from dropping too low?
Relative humidity. This is accomplished by evaporating water by adding the latent heat of the vaporization.
How do you avoid thermal bridging at the roof structure?
Roof insulation is placed entirely above or entirely below the supporting structure.
How do you convert SHGC to SC?
SC equals SHGC divided by .87
How does SHGC differ from SC?
SC is the ratio of radiant heat gain through a given type of glass relative to 1/8 inch single clear glass. SC is still a useful concept for comparing glass types
Vapor pressure difference is take Layton heat flow as temperature difference is to what?
Sensible heat flow
What is a form of energy that flows whenever there's a temperature difference?
Sensible heat.
What is the measure of the amount of heat required to raise the temperature of a given mass of material by 1°?
Specific heat
What are the three basic water systems?
Storage tank water heater Circulating storage water heater Instant/ tankless water heater
What does A stand for in the design heat loss formula?
Surface area of the envelope component
Sensible heat flow results in a change in what?
Temperature
What are the two primary means of calculating the infiltration air flow rate during design?
The air change method and the crack method
What does🔺t stand for in the design heat loss formula?
The design temperature difference between the outside air and the inside sir
What is the (SHGC) solar heat gain coefficient based upon?
The performance of the entire glazing unit not just that of the glass portion.
What information is necessary to calculate the design of heat loss through buildings envelope?
The rate at which heat flows through each of the elements. The area of each of these assemblies The design temperature difference between inside and outside
Emittence
The ratio of the radiation admitted by material to that emitted by a black body of the same temperature.
What factors influence the U factor?
The size of the air gap between glazing's, the coatings on the glazing's, the gas filled between the glazing's, and the frame construction.
Greater density will permit what?
The storage of more heat.
What is heat gain?
The total instantaneous heat flow.
What is an indicator of the ability of a fixed volume of material to store heat?
Thermal capacity.
What is the variation in temperature through a cross-section of the construction assembly called?
Thermal gradient.
What is the key determinant of steady-state heat flow?
Thermal resistance.
What is the job of the thermal envelope analysis?
To ensure that the proposed envelope will meet the design intent and criteria.
What is the sum of sensible and latent heat flows?
Total heat flow.
What does U stand for in the design heat loss formula?
U factor for a given component
What is the one overall property that expresses the steady-state rate at which heat flows through architectural envelope assemblies?
U-value
The difference in what is the driving force behind water flow through components of an intact building envelope assembly?
Vapor pressure.
The less permeable a material is the greater the resistance to what?
Water vapor flow.
Where does the dewpoint usually occur?
Within the insulation layer
What three types of heat flow are usually of primary interest?
design heat loss design heat gain An annualized heat flow
What is heat transferred between in conduction?
from molecule to molecule
What variables will affect design cooling load? The palate?
orientation tilt of an surface reflectance thermal capacity solar heat gain coefficient of a transparent/translucent assembly Shading Heat gained from occupants Heat gained from equipment
What kind of heat does U factor address
sensible heat
Materials with low permanence are termed what?
vapor retarders