Air Conditioning Applications

-Equipment (process) cooling

-Comfort cooling

Purpose of air conditioning

-To control: -Temp (Heating/Cooling)

-Air cleanliness

-Humidity control

-Air movement

*Note: The above can be accomplished by using either single zone or multi-zone control.

*Note: Air movement can be accomplished by using single duct distribution, dual duct distribution, multi-zone, or terminal re-heat systems which in turn may be constant volume or variable volume air systems.

Four Basic Types of HVAC Systems

•  All Air

•  Air Hydronic

•  All Hydronic

•  Unitary

•  All Air

-Supplies air only to conditioned spaces or zones by some type of duct system

-Duct system can be: -single zone -terminal re-heat

-Multi-zone -constant volume or variable volume

-Dual zone

(2) Air Hydronic

-Supplies air to conditioned spaces or zones as well as water to conditioned spaces or zones (parameter heating) fan coil units.

-Duct system can be: -single zone -terminal re-heat

-Multi-zone -constant or variable volume

-Dual duct

-Water system can be: -two pipe

-Three pipe

(3) All Hydronic

-Used where duct space is not available

-Supplies water only to conditioned spaces or zones by the use of special terminal units

-Terminal units can be: -fan coil

-Unit ventilators

-Valance units

-Water piping system cab be: -two pipe

-Three pipe

-Four pipe

(4) Unitary

-Self contained packaged units (normally an all air system)

-Arrangements: -single package

-split package: -2 split

-3 Split

Types of Duct Construction

-Round ducting -Rectangular

-Square -Flexible (fiber glass covered with foil)

Duct Insulation

-There are two reasons to insulate duct.

1. Sound

2. Heat transfer

Parts of the Duct System

-Outdoor air -return air

-Exhaust air -supply air

-Mixing plenum

Main Plenum Houses Major Components

-Heating coil -humidifier section

-Cooling coil -pre-heat coil

-Fan section -re-heat coil

-Filter section

Dampers or Air Flow Control ? Reference = SMAKNA page 1.3

-Parallel blade

-Opposed blade (most effective)

-Used for: -fresh air intake min. 20% fresh air

-Exhaust air (determines room press)

-Mixed air

-One supply

*Note: Louvers unlike dampers are normally fixed or adjust manually

Definitions

Building related illness: a specific illness with a known cause that is the result of exposure to an indoor agent

Health: A stat of complete physical, mental and social well being and not meekly the absence of disease

Indoor air quality: the physical, chemical and biological characteristics of inside air

Sick building syndrome: A condition in which occupants complain of a set of symptoms that can not be related to a specific cause but are alleviated when occupant leaves the building

Thermal comfort: A state of mind in which a person feels satisfaction with the thermal environment. Includes temp, humidity, air movement, clothing and activity level. ?(Satisfy 80% = good)

Ventilation rate: The amount of outside air that is combined with return air that is supplied to the interior space

Poor indoor air quality: Air quality for occupied spaces is becoming a major concern in today's society. Poor air quality results in a loss production (employee illness) as well as equipment failure

Results of Poor Indoor Air Quality ? Ref: SMACKNA – Basic H-VAC systems (A-E)

-Cooling and heating coils clog

-Hazardous fir conditions may be created

-Expensive duct cleaning

-Diffuser streaks created

-Illumination is affected and reduced (lights)

-Employee discomfort and illness

*Note: The key to good indoor air quality is proper filtration which is accomplished by the use of:

Air Filters

- Mechanical

- Electric

These two classes are designed to remove particulates (suspended particles), either solid or liquid

Sick Building Syndrome and Related Complaints

-Factors that affect indoor air quality:

• Temp and humidity 72-78°F Winter (35°F) Summer (55°F) RH
• Carbon dioxide from fossil fuels
• Carbon monoxide tobacco smoke and car exhaust
• Formaldehyde:
• Unseal plywood
• Particle board
• Form insulation
• Glues
• Carpets
• Furnishings

• Particular:
• Water residue
• Water inlets
• Carpets
• Duct insulation
• Volatile Organic Compounds (VOCs):
• Copt machines
• Cleaning materials
• Perfumes
• Hair sprays
• Solvents
• Computers

• Microbial Matter:
• Stagnant water in H-VAC
• Humidifiers
• Cooling Towers
• Drain Pans

The following general indications help to call attention to pollutant sources:

• Over cooling
• Unsanitary conditions
• Dust accumulation (house keeping)
• Moisture problems (visible fungal growth)
• Staining or discoloration of ceiling tiles or walls
• Presence of chemical substances
• Odor (see below)

Odors as Problem Indicators in Office Buildings:

Forms of Suspended Particles

Types of Filters
- Viscous Impingement Filters

•  Adsorption

•  Class 2 non fire resistant

•  Types: Disposable (bulk frame), self renewable

- *Note: Material used for disposable/ self renewable filters is normally

•  Fiberglass

•  Animal hair

•  Cellulose fiber

- *Note: Material used for cleanable is:

•  Metal panels

•  Fine mesh screens

•  Combination of both

- *Note: The above type of filter will have an adhesive coating which is often mineral oil thus the name viscous.

-Note: ASHRAE dust efficiency is 5 to 25% (poor). Normally used as a pre-filter only

- Dry Media Filters

•  Adsorption

•  Class 1 fire resistant

•  This type of filter has a tacky coating that viscous impingement filters have.

- Types:

•  Plain panel

•  Extended surface/ pleaded

•  Bag filter: Cartridge/ cube/ pocket

•  Renewable

-*Note: In addition dry media can be impregnated with carbon or zeolite for additional removal of organic based odors such as:

•  Cooking

•  Cigarette smoke

•  Ozone

•  Disinfections

•  Mold + mildew

•  Paint fumes

•  Waste / refuse

-Uses: Removal of some solid contaminations

-*Note: ASHRAE dust spot efficiency is 15 to 99.99%

Can be purchased as

•  Low efficiency

•  Intermediate efficiency

•  High efficiency (HEPA: High efficiency Particulate Air)

Air Washers or Scrubbers

•  Adsorption

- Types:

•  Water Sprays

•  Wet cooling Coil

-*Note: These are highly effective for removing liquid particulates

Ultra Violet Light

•  Most effective for killing bacteria as well as viruses

Heating Equipment
-Hot water (At 30 PSIG through converter, Max temp 250°F)
-Steam (Low press. System below 15 PSIG)
-Electrical heat



HVAC Heating systems
-Hydronic distribution Systems

Types of Systems

Air Water Systems: Hot water or steam is supplied to central air handlers, individual fan coil units or building convection units

Temp Classifications
Low Temp Water (LTW): Normally operates at 30 PSI with a max temp of 250°F

Medium Temp Water (MTW): Normally operates at 130PSI with a max water temp of 350°F

High Temp Water (HTW): Normally operates at 300PSI with a max water temp of 450°F

Dual Temp Water (DTW) Uses both hot water and chilled water

Chilled Water Systems (CWS): Normal operating pressure 125 PSI with a max water temp of 40 to 50°F

Types of Hydronic Heating Systems

•  Series Loop

•  One Pipe

•  Two Pipe (Direct or Reverse Return)

•  Three Pipe

•  Four Pipe

Humidity Control
- Recommended humidity levels 35 to 50% comfort/ OEM recommendations for equipment cooling

- Importance:

• Humidity Above: When levels vary above limits studies have shown that bacteria/ viruses/ fungi and other organisms become more active
• Humidity Below: Dry air tends to draw moisture out of carpets/ furniture/ woodwork/ plants as well as people. There is also an increase of static electricity

-Dehumidification:

• Cooling Coil (normal operation)
• Cooling Re-heating (Dehumidification only)
• Descant system

Humidification:

Air Movers
-Definition: A fan is a device that moves air. With out it no air handler system will operate. Its function is crucial to proper air cooling and comfort conditioning

- Fan Construction:

• Impeller
• Frame or Housing
• Prime Mover

-Impellor: Is that part that pushes the air and must be rotated by a prime mover. Normally an electric motor. Classified according to the direction of air flow through the impeller.

• Centrifugal Flow = Flow outward from axis of impeller
• Axial Flow = Flow parallel to the axis of impeller
  

- Types of Impellers:

• Propeller
• Fan disk
• Fan wheel (Axial Flow)
• Vein Axial (Laminar Discharge) – Incorporates inlet guide veins
• Tube axial (Spiral Discharge)
• Fan Wheel (Centrifugal)
• Backward Curve or Inclined
• Forward Curve or Inclined
• Radial (Squirrel Cage)

Distribution Systems

-Low Velocity: Below 2000 feet/ Min

-High Velocity: Above 2000 feet/Min

Application of Various Types of Impellor Designs
- Selection is based on fans ability to overcome system resistance and create enough velocity for proper movement of air

-In order for a fan to accomplish the above the fan itself will generate 3 diff. pressures

• Velocity Pressure
• Static pressure
• Total Pressure

- Static Pressure : This is the outward force on the duct created by the system resistance such as: -Filters -Cooling Coils

-Ducting -Heating Coils

-Diffusers

- Velocity Pressure : This is the pressure delivered by the fan to actually move the air down the duct system to the conditioned space or zone

- Total Pressure : Sum of Static press + Velocity press

-Note*: All three of these pressures are created by the fan and are measured in Inches of Water - Read by a manometer. Inches of water column is used to more easily read very small pressures above and below atmospheric created with system ducting.

• 1 inch water column = 0.036 PSIG
• Also: A magnehelic measures press. Example, pressure drop across a filter

-An increase in static pressure will result in a decrease in system velocity pressure which will result in an overall decrease in CFM delivered by the fan

-Fan Performance: The performance of a fan is its ability to generate the required static pressure for the system its applied to yet maintain the required velocity pressure to ensure delivering the required CFM


Fan Selection
-Based on:

• System Size
• 1. CFM Required
• 2. Total Resistance (Static Press)
• Space Availability
• 1. Axial Flow (Limited Space)
• 2. Centrifugal (Unlimited)

-Forward Curve:

• Overloading
• 20,000 CFM @ MAX 4” Static

-Backward Curve:

• 20,000 CFM @ 3” Static + (Plus)

-Axial:

• 50,000 CFM @ 3” Static + (Plus)

Fan Arrangements

-Draw Through:

• Fan located at outlet of main plenum
  

-Blow Through:

• Fan located at inlet of main plenum
  

-*Note: Can be a:

• 2 Fan system: Separate supply and return fan
• 1 Fan System: One fan for return + supply air

Terminology
- Overloading Fan Type : On a sudden decrease in static the prime mover will develop excessive HP and will overload

- Non-Overloading Type : On a sudden decrease in static the prime mover will not develop excessive HP thus will not overload

- Fan Curves : for Backward and Forward Inclined

Fan Laws
-#1 States: The amount of air delivered by a fan will vary in direct proportion to the speed of the fan.

• Formula: New RPM ={(New CFM) x (Existing RPM)} ÷ (Existing RPM)

-#2 States: The resistance of a system varies directly with the square of fan speed.

• Formula: New Static = (Existing Static) x {(New RPM) ÷ (Existing RPM)}²

-#3 States: The power varies directly with the cube of the fan speed

• Formula: New HP =(Existing HP) x {(New RPM) ÷ (Existing RPM)}³

-Example:

-Using the fan laws we will calculate the fan speed / static pressure and HP required to deliver 15000 CFM that the system was designed to operate/ deliver

-Fan Law #1: 1063 RPM = {(New CFM) x (Existing RPM)} ÷ (Existing RPM)

-Fan Law #2: 4.2” Static = (Existing Static) x {(New RPM) ÷ (Existing RPM)}²

-Fan Law #3: 17.5 HP = (Existing HP) x {(New RPM) ÷ (Existing RPM)}³

-Therefore The existing motor if operated at 1063 RPM would develop 4.3 inches Static/ would develop 17.5 HP and deliver 15000 CFM of air.


Basic Components of All A/C Systems

Centrifugal Chillers
-Low Pressures: R-11, R-113, R-123A

-Medium Pressures: R-22

-High Pressures: R-12, R-114, R-134A, R-500

Major Components