HVAC

Below find detailed information concerning each of the following topics:

 

HVAC Design Criteria

Important criteria to be considered while designing for HVAC.

  • Geographical Location
  • Target Temperatures
  • Number of People
  • Equipment - that generates heat
  • Traffic through the exits
  • Ambient Temperature ranges
  • Percentage of Glass and tint
  • Amount of Lighting
  • Insulating values of the building

Air Conditioning:

  • One ton of air conditioning is equal to 12,000 BTU's.
  • General Formula for an interior office is 1 ton per 400 - 500 square feet.
  • Add 800 BTU's per person when high room occupancy is a factor.
  • When using this formula place careful consideration on the criteria listed at the top of this section to adjust the formula as necessary. Air conditioners generally have thermostats so as a rule a little more BTU's than not enough is better.
  • Exterior buildings such as guard buildings, that have direct sun light, maximum glass for visibility should have 1 ton per 150 square feet. Add to that active traffic through the door or constantly opening a sliding glass window and that formula could change to 1 ton per 75 - 100 square feet.

---------- TOP ----------

 

Heating / Venting

Note: All general formulas listed are based on normal conditions and are to be used for estimating requirements. In cases of extreme or unusual conditions a more accurate figure can be determined by a qualified engineer or architect.

Heating:

  • General Formula = 7 watts per square foot
  • example 10' x 10' room = 100 square feet
  • 100 sf x 7 watts = 700 watts required for heating.

Venting:

In general, venting occurs in most rooms through the air conditioning system, however there are occasions when additional venting will be necessary. For example lunch rooms or conference rooms where smoking is permitted or kitchens or other areas that may generate smoke or rest rooms. The design requirements will either be listed as the total CFM's (cubic feet per minute) required like 200 CFM's, which is how venting/exhaust fans are rated or a fractional formula like .15 CFM's per cubic foot where you would multiply the cubic feet (L x W x H) by the fraction (.15) to determine the total requirement or it may be listed as the air changes required per hour. Air changes per hour is simply the number of times "old air" will be replaced by "new air" in 60 minutes.

  • example 10' x 10' x 10' high room = 1000 cubic feet
  • 3 air changes per hour is required (1 time every 20 minutes)
  • 1000 cubic feet X 3 air changes = 3000 cubic feet
  • 3000 cubic feet / 60 minutes = 50 Cubic feet per minute

---------- TOP ----------

 

Types of A / C

1. Wall or Window Units:

  • Locate them high on the panel when possible.
  • Electrical Outlets are usually on the right.
  • Center the unit in the room or use 2 small units rather than 1 large unit to cool a large room.
  • All units form condensation, however the typical design is to have an evaporator pan to handle this. If this is not adequate an alternate drainage hose may be needed.

 

2. Central Air Conditioning:

  • For large offices this is the preferred choice.
  • Central Air is more cost effective and quieter.
  • The Duct work can be placed in the "plenum area" if a minimum of 6" - 12" of space is available between the ceiling grid and the lowest beam, greater height may be needed for larger areas or where more air flow capacity is needed. If this area is not adequate then placing the duct on top of the roof is an option.
  • In general 1 Air supply register is required per 200 square feet.
  • Offices that do not have return air grills should have louvers in the doors or the doors should be cut short to allow for air flow.

 

---------- TOP ----------