Design

Each piece of equipment from the design stage through the selection and installation should be maximized to give the customer the most economical and efficient system you can for every dollar he has invested

Step#1: Load Estimating
-Cooling
-Heating

-2 Methods of estimating
-Block load
-Room by room

Accuracy: Blessing or Curse

Estimating The Air Conditioning Load

Survey the Structure: To determine the best method of installing the system

Building Orientation:
-Relationship to the sun
-Wind direction
-Location in relation to the other buildings
-Surrounding trees

Building Size: For conduction and convection gains or losses

Building Shape: For air distribution and lay out of duct system

Construction Materials:
-Wall
-Roof
-Floors

Glass Area:
-Percentage (%)
-Type
-Affecting factors

Infiltration + Exfiltration:
-Air coming inside + air going outside
-Door location
-Door construction
-Number of doors

People Occupancy

Equipment Located With In The Structure

Ventilation Requirement

Equipment Location

Utility Services

Building Codes



Principals Of Load Estimating For Air Conditioning Systems

Heat sources for air conditioning load calculations

Inside Conditioned Space
-People
-Appliances
-Lighting

Outside Conditioned Space
-Transmission gains
-Walls
-Roof
-Solar Gains
-Windows

Additional Loads
-Ceilings
-Floors
-Infiltration gains
-Cracks in building envelope

Outside Heat Sources (Transmission Gains)
-Walls/ Roof
-Affected by materials used in construction/ the total area of the surface/ solar effects as well as the temp diff. across the material

To Determine the amount of heat transfer thru the buildings surfaces (by conduction) the following formula is used.

How To Reduce Conduction Gains Through Walls + Roofs

It should be noted that any increase beyond 4” will not significantly improve overall U-Factor of structure

2. Roof Materials
Light Construction – Wooded frame – (18 BTU's sq ft) max no insulation
Medium Construction – 4” Concrete – (19 BTU's sq ft) max no insulation
Heavy Construction – 6” Concrete – (15 BTU's sq ft) max no insulation

The above info is taken at peak solar gain times, approx. 3:00 pm. in the afternoon

Solar gains can be reduced by two methods:
-Shaded roof = reduction by 75%
-Roof sprays = reduction of 65%

U Factors for typical construction types
-Residential wall = 0.25
-Residential roof = 0.31
-Commercial wall = 0.33
-Commercial roof = 0.40

Transmission Gain Calculation
-Find the total heat gain through a residential wall with the following dimensions.
-Length = 20'
-Height = 8'
-Outside ambient temp 85ºF
-Inside room temp 75ºF

Outside Heat Sources (Solar + Conduction Gains)

Windows
The Solar heat entering a structure through glass is immediately absorbed in the room. The amount of solar gain through the windows is determined by the TD surface area and type of glass used in its construction. Conduction gains through glass will also use the same formula

To determine the amount of heat gain (solar as well as conduction) the following formula would be used

BTU's/Hr = Overall co-efficient of heat transfer x surface area x TD

Transmission/ Window Gain Calculation
-Find the total heat gain through a residential wall with the following dimensions:
-Length = 20'
-Height = 8'
-Outside ambient temp 85ºF
-Inside room temp 75ºF
-There are two windows located on this wall 2' x 4' ordinary glass no shading
-U-Factor = 0.25 for transmission gain on walls
-U-Factor = 1.13 for transmission gain on windows

Outside Heat Sources (Solar + Conduction Gains)

Floors
Normally floors would be considered to be a heat loss for heating load calculations if it is a slab or basement construction. However if a unconditioned space is located below the floor level which is conditioned it would be calculated in a cooling load calculation

Air Change (Infiltration Load) (Exfiltration)

*Air change is the continuous exchange of air between every building and its surrounding

-This air change is the result of two different processes: Ventilation + Air Leakage

Ventilation: Is a controlled air change. Can be provided by
-Bathroom fans
-Kitchen fans
-Exhaust fans
-Dryer vents

Air Leakage: Is an uncontrolled air change as air flows through
-Cracks
-Structural joints
-Window frames
-Door frames

*Another source of heat that must be considered is infiltration loads or losses. This is the air that enters a building due to cracks around windows and doors. The degree of infiltration depends on quality of construction, doors being opened and also wind velocity.

Ventilation
Ventilation standards are governed by ASHRAE: American society of heating refrigeration and air conditioning engineers. These standards are set to dilute unwanted odors and replenish used oxygen with in the conditioned space

Inside Heat Sources (People, Lights and Appliances)

People
Heat gain from occupants is based on the average number of people expected to be present to be present in the building as well as the activity they are involved in. Sensible + latent heat loads are present (Rule of thumb 330 BTU's/ hr total heat)

Lights
The load from lights is substantial and must be calculated in any load calculation
Incandescent Lighting: 3.4 BTU's/ watt
Florescent Lighting: increase lighting load by 25 % (ballast)


Appliances
Heat gains from appliances located with in the conditioned space must also be calculated. They can be a sensible or latent load