Unit 42 Flashcards
What are disadvantages of oversizing equipment
1-cost more to manufacture, purchase, install and maintain
2-cost more to operate because of large motors and other electrical loads
3-requires larger air distribution systems which cost more
4-will cool or heat quicker resulting in more system starts and stops
5-poor dehumidification
6-could increase mold growth
Disadvantages of under sizing equipment
1-Will not maintain space temperature
2-long run times
3-power bills go up
4-strips run more in winter
In summer we have heat blank to the structure
Gain
In the winter we have heat blank to the structure
Loss
To size equipment properly the process is called
Heat loss heat gain Manual J
2 methods of calculations used on structures
Total envelope and room by room
Why do we perform load calculations on houses
To have proper size heating and air systems
To match the house for temperature and humidity requirements
What is the rule of thumb for sizing HVAC systems in this area
600 square feet per ton
Name 4 things that must be considered before a load is done on the structure
How accurate for the result have to be
How accurate does the temperature control need to be
How critical does the humidity control need to be
Is an equipment rebate being applied for
Give 6 disadvantages in using a rule of thumb to size your HVAC equipment
Does not take into account the geographic location of the house
Type of material used in construction
Slope of the roof and the color of the roof and materials
Orientation of the hous
Types of windows and doors
Number of windows and doors
What is the disadvantage of using the manufacturers equipment simplified load sheet
May not be accepted where rebates are involved
What is the most accepted form of heat gain, heat loss in our industry
Manual J
What kind of problems could come about from a poor system design and end up in court
Could have structure damage
Mold related issues
Health related issues
Factors needed to calculate a load on a structure would be
The difference between the indoor and outdoor temperature
Type of construction materials used
The indoor design temperature for manual j for heating and cooling is
Heating-70
Cooling-75
What is design temperature for the summer and winter
Summer
Indoor-75
Outdoor 95
Winter
Indoor-70
Outdoor-24
What is the daily range
The average difference between the daily high and daily low temps for a given location
R value shows what
Thermal resistance of insulation materials, higher r values harder for heat to pass through
R value of 38 gives what U value
.026 1/38
How is the U value expressed
BTU’s per hour per degree Fahrenheit per square foot
List areas that heat can be gained or lost through the structure
Exposed walls, windows, doors, roofs, ceiling cavaliers, partition panels, below grade walls, slab and basement floors, floors above unconditioned spaces, cracks in the structure
What is sheathing
Relatively thin panel installed on the outside of the wall or roof framing and covered by brick, stone, siding or shingles
What is the gross wall area
Area of a wall before any windows or doors are cut into it
What is the net wall area
A term used to describe the area of the wall after the doors and windows are cut into the wall
What is the formula for heat transfer
Q= U value x TD x Area
Define the term below grade
Walls or portions of a wall that are below ground level
The term slab on grade is
The house is on a slab which is on ground level
Insulation around the perimeter is expressed in blank and not U values
F values which is btus per running door per degree Fahrenheit
What does the 1.08 represent in the CFM formula
It is a constant, 1.08xCFMxTD. Is an estimate of how many cubic feet of air are entering the structure each minute
ACH stands for
Air changes per hour
How do we determine the volume of a house
LxWxH. Once you find the CFMs then use formula 1.08xCFMxTD
The rate at which heat loss happens as air passes through a duct in an unconditioned space is determined by
Temperature of air in the duct
Temperature of the air in the unconditioned space
Amount of insulation on the duct work
What other internal heat gain do we have in a structure
Occupants Appliances Lighting Plants Fish tanks Other heat generating elements
Heat gain can occur in many ways which are
Through exposed walls Through doors Through roofs, walls, floors and ceilings Through windows From people, appliances, lighting Through cracks in structure Through duct runs through attic
The sum of heat gain on a structure is
Conduction Loads
Internal loads
Solar loads
Infiltration loads
Two things that are important when getting the heat gain factors for windows
Make sure you’re using the correct table
Get the correct orientation of the windows
List other things that would impact the solar load on the house
Amount of shading
Overhangs
Extras on the window itself
Internal shading
When we are calculating heat gain what is the estimate figure we use for people
Number of bedrooms plus 1
How many BTUs of sensible and latent is used for people
Total heat gain is 430 BTUs
Sensible 230 BTUs
Latent 200 BTUs
