Residental Hvac Design Flashcards
What should be taken into consideration when selecting a blower ?
Select a blower speed that will maintain proper tempature rise and correct cfm distribution on both cooling and heating cycles as well as the proper air circulation rate
What should the heating output percent be ?
100-140%
What should the cooling output percent be?
80-125%
What is the recommended airflow per ton of cooling ?
400cfm
What are some factors u should consider when designing a duct system ?
Ducts running through unconditioned spaces
Proper duct size
Zoneing systems
Combustion and dilution air
What is the supply air ratio for an unfinished basement ?
1 supply air for every 430ft2
What is the minimum undercut per cfm ?
30cfm
60cfm
90cfm
120cfm
30cfm = 1/2”
60cfm= 3/4”
90cfm=1”
120cfm=1 1/4”
What does the Alberta building code state about return air ?
Must have one return air per floor and basment should only be 50% and any room that has atkeast one half of the floor area above an unconditioned space must have return air
Where should return airs never be installed ?
Kitchens
Bathrooms
Laundry rooms
Utility rooms
Enclosed crawl spaces
Should also never be installed back to back in same stud space because light and sound transfer
What are two things to consider with ventallation air ?
Fresh air size
Mixed air temp
How far should the fresh air connection be from the blower ?
Minimum 10 feet
What temp should air circulated through the blower never drop below ?
60 degrees F
For a 2x4 opening what is the number of cfm that flows through it ?
120cfm
For a 2x6 opening what is the number of cfm that will flow through it ?
180cfm
What are four factors to consider when dragging a duct system ?
Proper duct size
Duct passing through unconditioned spaces
Zoneing for house
Combustion and dilution air
What is an acceptable air velocity for the main trunk ?
700-900fpm
When should a walk in closet have a supply ?
When the closet exceeds a heat loss of 1000btu
What’s the result of installing a furnace to large?
Short cycling
Before selecting a furnace what must be done first ?
Heat loss calc
What must be done if duct is running through an unconditioned space ?
Seal and insulate the duct
Where should the Vapor barrier be located when insulating ducts ?
On the warm side
If a supply air measure more than 50ft in length what should be done to the cfm at the register ?
Should be sized to handle 10% more cfm than originally designed
How far off the wall should supply outlets be located ?
8” or 20cm
Why should we install supply register off the wall and not flush with wall ?
So it does not interfere with the drapes
What must crawl space supply runs have installed ?
Lockable dampers or diffuser
Why can a vertical return air not serve more than one floor ?
Prevent cold air from going floor to floor
What is the design static pressure to be used for a house ?
1/2”of wc
How do you determine cfm per return air opening ?
Floor return air flow rate divided by number of inlets
What increments does return air go up in?
0 turbelence at the closest return air to a taper and then up 40’ from there
What cfms should a transition be used at ?
Supply every 200-300cfm
Return every 300-400cfm
What is the aspiration effect ?
The negative effect velocity has on the ability of rushing air to enter the branch duct on supply
What 3 things are airflow rates based on?
Heating cfm
Cooling cfm
ACR
What airflow rate do you use ?
The largest of the 3
In areas where the dry bulb tempature exceeds 81 what must be done ?
The air volume for cooling shall be incorporated
How many heat runs are required for a heated crawl space ?
One for every 80m squared
What should the Tempature never exceed on supply air ?
158 degrees Fahrenheit
70 degrees Celsius
What is the average pressure drop at a grille ?
.04
How do we determine joists to trunk opening size ?
Return air branch size x 2
1 kw =1.341 How many btu?
3412 btu
