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- Cooling coil GPM = Total capacity (Btu/hr) / 500 / Delta T
- Electric Heat (kW) = ((CFM x 1.085 x Detla T) / 3.413) / 1000
- Mixed Air Temperature = ((RA cfm/SA cfm) x RA Temp) + ((OA cfm/SA cfm) x OA Temp)
- Room air changes (per hour) = (Room volume x Number of required changes) / 60
- Btuh = cfm x 1.085 x Delta T
- Place shut-off valves in locations to avoid shutting down entire systems if one branch goes down.
- Avoid locating equipment and valves above gyp ceilings if possible.
- No piping over electrical rooms or data rooms/closets.
- Indicate routing and slope of condensate lines.
- When you are showing floor drains under ice makers or any other equipment, verify clearance underneath equipment. Verify that there is at least 3” clearance.
- Minimum 2”ø waste or vent under slab.
- First thing: Check architectural plans for walls that go to structure.
- Loads: Call architect to verify that glass shop drawings match that of installed.
- Loads: Verify lighting watts/ft2
- Verify fan terminal unit placement and type for noise consideration. Think about heating contactors. Magnetic contactors are louder than mercury type. Verify boxes are not over return air grilles or offices.
- Verify fan terminal unit placement and type for accessibility. Even if walls are indicated as not going to deck, the studs may go do deck and gyp may stop at 6” above ceiling. Fan terminal units typically require bottom access as well as side electrical service clearance.
- If possible, put balancing damper for gyp mounted diffusers in adjacent lay-in or other accessible areas. Neck mounted blade volume dampers can be noisy. Consider cable operated dampers if necessary.
- On multi-floor buildings, tag equipment by floor (i.e. VAV 7-1, VAV, 8-1)
- Locate return air transfer openings towards RA source.
- Space O/A intakes and exhaust/vents 15 feet apart. 10 feet is required, but use 15 feet to be safe.
- Sensible capacity is typically 80% of Total capacity.
- For local projects (Kansas City), design outdoor equipment at 105°F.
- Low pressure fuel gas systems are less than 1.5 psi.
- High pressure fuel gas systems are more than 1.5 psi
- Natural gas heating value: 1,000-1,100 Btu/ft3
- Liquid petroleum heating value: 2,500 Btu/ft3
- (For an outdoor air unit) specify catalogued MBH capacity instead of actual design capacity. If you specify 252 MBH and the units are only available in 250 or 300, the equipment rep will go with the larger size to cover his ass. The larger unit will be over sized and hard to control to design conditions.
- Specify SCR control instead of staged control. There is no cost difference and you get greater control modulation with SCR.
- Always specify a single point power connection.
- Specify mercurcy switches instead of magnetic contactors where noise issues are critical.
- (For an outdoor air unit) consider UL listing of a pieced together system as opposed to a packaged unit.
- Use 12x24 RA grilles in small rooms. 24x24 overpower the look of the ceiling.
- When using supply slot diffusers for returns, use the same diffuser, but tag and schedule as ‘Rx’.
- Only use 6”ø diffusers in areas that will not change in the future. Storage rooms, small offices (100 CFM or less), etc. are okay. Do not use in open office areas where airflow requirements could change in the future.
- Perforated return air grilles: 24x12; 0-600 CFM max., 24x24; 600-1000 CFM max.
- Use 12x12 diffusers in lay-in ceilings for airflows of 75 CFM or less. You won't get any throw out of a 24x24 at that low of an airflow.
- Main supply duct velocity: 900 FPM Max.
- Branch supply duct velocity: 600 FPM Max.
- Supply register velocity: 500 FPM Max.
- Max. supply duct static pressure: 0.10” W.C.
- Main Return duct velocity: 700 FPM Max.
- Branch return duct velocity: 400 FPM Max.
- Return grille velocity: 400 FPM Max.
- Max. filter media (return air) velocity: 400 FPM Max.
- Max. return duct static pressure: 0.08” W.C.
- Size return air transfer openings at 700FPS max. velocity.
- When possible, use 14x8 or 14x10 RA boots to fit between studs.
- Oversize return air openings and return air boots.
- Medium pressure duct: Size at 0.2 (Friction) then verify that Velocity is at or below 2000 FPM
- Low pressure duct: Size at 0.08 (Friction) then verify that Velocity is at or below 750 FPM
- When possible, keep duct size ratio a minimum of 3:1
- North perimeter office: 1.25 CFM/sq. ft.
- East/West perimeter office: 2.0 - 2.25 CFM/sq. ft.li>
- Interior rooms & open office areas: 0.75-0.8 CFM/sq. ft.li>
- Interior conference rooms 1.25 CFM/sq. ft.
- No less than 100 CFM in an office, regardless of size.
- Figure 12.5 CFM supply air per person.
