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2011 - Volume 1 Issue 2
Casas Bonitas
New Home Construction
Article: Bob Skolnick
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Your air conditioning system is responsible for your comfort by maintaining a desired temperature in your home, but also your health by keeping your air fresh and free of organic compounds.

The air conditioning system in your home not only is responsible for you keeping comfortable by maintaining a desired temperature, but also your health by keeping your air fresh and free of organic compounds. Refrigerated air conditioning systems will remove moisture from the air and de-humidify your home. Air conditioning systems are the highest consumers of energy in typical home. In this climate zone the primary energy consumer is the air conditioning system. How efficiently your heating and cooling system operates determines the energy consumption and your operating cost in the form or a monthly electric and/or gas bill.

    Photo Captions

1.) Air Conditioner or
Heat Pump

2.) Thermostat

3.) Furnace or Air Handler

4.) Filtration Device

5.) Germicidal Light

6.) Indoor Coil

7.) Humidifier

8.) HEPA Bypass
Filtration System

9.) Energy Recovery Ventilator

10.) Supply Duct

11.) Return Duct

12.) Dehumidifier System

13.) Residential Generator

14.) Lennox LZP-4 Zoning System works with standard heating and cooling systems to provide precise comfort throughout the home, throughout the year.
  "Energy Star requires that
heating and cooling duct-
work be covered by the
ceiling insulation, which
effectively puts the ducts
in the thermal building

Sergio Cuartas,
BIC Homes
  "Tight homes require
ventilation for sustaining
the quality of breathable
air, and a heat recovery
ventilation system (HRV)
will accomplish that while
maintaining the energy
efficiency of the home."

David Coyle,
Coyle Associates

Aire Serv Heating &
Air Conditioning

924 W Picacho Ave.
Las Cruces, NM

Sun City Plumbing & Heating
560 N 17th St.
Las Cruces, NM 88005

Mechanical Technologies
211 N Cotton St.
El Paso, TX 79901
The air conditioning unit is called to serve a specific size home under a specific set of conditions. Each home is unique in design and use by the homeowner’s family. It is essential that the air conditioning unit be designed and sized to exactly fit the circumstances. Your builder will consult with a company that specializes in installing heating and cooling systems and the supporting ductwork. A load calculation will be conducted for the cooling unit by entering data into a computer model and running a profile called a Manual J load calculation. This modeling takes into consideration many areas. A few key entries are the square footage of the living space area, the ceiling heights, the type of insulation used in the walls, the type of roof (pitched or flat), the insulation applied to the inside of the roof and the orientation of the house to the south and west where the strongest sun irradiates a home. The calculation considers the number of windows, the type and rating of the windows, the number and type of doors and the appliances to be installed in the kitchen, laundry room and bathroom. An entry is made for how “tight” the house is by design and by construction. The calculation also requires the sizes and uses of rooms. The load calculation formula is complex and is dependant on the builder and homeowner following through on the stated elements that were provided by the heating and cooling professional to create the load calculation.

Once the Manual J load calculation is complete, the heating and cooling professional will know what size of air conditioning unit to order for your home. Air conditioning units are sized in tonnage. It is essential that your unit is exactly sized for your needs. When an air conditioning unit comes on and runs for a short period, it is called short cycling (the unit is too large for the need and runs inefficiently). Short cycling hurts the equipment and causes unusually high energy consumption and does not effectively remove humidity. It also causes the unit to not effectively remove the humidity in the home interior. A properly sized unit will run longer cycles with lower horsepower demand on the compressor.

In certain circumstances there is a need for more than one air conditioning unit for the home, requiring a system called zoning. Typically when the square footage of the home exceeds 2000 square feet, zoning with one unit or adding a second unit is recommended. Often when there are two stories to a home a second unit is specified and sized for the upstairs rooms. Zoning requires thermostats in the destination rooms and in-line duct dampers that are electronically controlled to deliver air to different rooms of the house on demand and possibly at different temperature settings. The thermostat control systems for today’s equipment are very sophisticated. They can deliver cooled air to within one half degree of the setting on the thermostat. Each thermostat communicates individually with the central air conditioning unit.

Once your professional has made recommendations on the unit(s) size and method of delivery of cooled air, you have several other important considerations. Air conditioning systems are not a shelf product. They are assembled at the manufacturer based on your order specifications and then shipped to the heating and cooling professional for installation in your home. One important element is the type of blower motor to deliver the cooled air through the ducting. Most units come with a standard blower. You have a choice of ordering your unit with a variable speed blower, and I highly recommend this additional investment, which likely will add about five to six hundred dollars to the cost of the unit. A variable speed blower motor steps up and steps down the delivery of air when the cooling unit cycles on. This option results in more stable temperatures in the home and a more efficient fan operation, thereby saving you operating costs. A variable speed blower also provides a quieter air conditioning system.

Another key consideration is ordering your air conditioning unit with an in-line air filtration system. Because of the wind born dust in this area, many volatile organic compounds can come into the house, either through the air exchange that takes places naturally when a door or window is opened or by design through your air conditioning system. An air filtration unit can be added by the manufacturer at the time you order your unit(s), which will remove 99.8 percent of the foreign particles from your home. You will have a filter to replace about every six months.

Finally, it is important where the air conditioning system is placed, whether on the roof or on the ground adjacent to the house. Roof mounting exposes the unit to direct sunlight radiation all day long. A ground-mounted unit will be in the shade at least half of the day, especially if the house roof design provides for an overhang.

The heating and cooling professional will use all of the data and the size of the air conditioning unit to design the delivery requirements of each room. Kitchens, laundry rooms and bathrooms have different requirements than bedrooms or studies. Knowing this allows the heating and cooling professional to design the duct work which is the system to deliver the cooled air to each room of the house. This is done by a manual D calculation. All ducting needs to be properly sealed and insulated. Some builders will place an aluminum shield around the ducting and enclose it with dry wall material to improve its ability to maintain cooled air at the desired temperature.

A part of the duct design takes into consideration the return air and new fresh air requirements. A home needs a full exchange of fresh air at least eight times per twenty-four hour period. Bedrooms, where doors often remain closed, most definitely need return air ducting to ensure air exchange. Much of this air exchange happens naturally. It is important to understand that your air conditioning system is the circulation and re-circulation of cooled air and fresh air under pressure in your home. The tighter the house construction, the lower the air loss through the walls, windows, doors and ducting, but there will be air loss and the lost air needs to be replaced to keep the system in balance. Also, exhausts and vents in kitchen and bathrooms expel air and that air loss needs to be replaced. In the furnace closet, a Heat Recovery Ventilation (HRV) system is installed to transfer exhaust air to incoming air during the heating season and from incoming air to exhaust air during the conditioning season to reduce the heating and cooling load. In essence, the system mixes the new fresh air with the ambient air inside the house prior to it entering the air conditioner. An Energy Recovery Ventilation (ERV) system provides similar results but also reduces the moisture in the air, resulting in a lower humidity level. At the completion of the duct work installation the heating and cooling company will perform a duct blast or pressure test to insure the ducting does not have any leakage. At the completion of the entire home, an energy rater can be called to perform a blower door test to determine the efficiency of the whole house in conjunction to the heating and cooling system.

What about heating your home? The heating of a home in this temperature zone is much easier than introducing cooled air. A separate gas furnace is an efficient and cost effective way to heat your home. Natural gas in this region is a very affordable energy resource and provides the energy to keep your home warm. If you do not want natural gas in your home, there are a few other options that can be considered such as ordering a heat pump with your air conditioning unit which allows your air conditioning unit to run in reverse and heat air. This uses electricity rather than natural gas and will cost you a lot more to operate during the coldest months.

Remember, bigger is not necessarily better and the objective for comfort, healthy air and a cost-effective operation is to have a designed and balanced system in a tight house. ///
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