This article is to help consumers make informed decisions about their air conditioning and heating system purchases so they can achieve the comfort, safety and performance they desire. This may be one of your biggest investments that will provide comfort to you and your family in your home for the next 20 years.
Equipment Purchases and Efficiency:
Your air conditioning and heating equipment are purchased separately. Similar to the way you would purchase a washer and dryer or a refrigerator and stove. But they are NOT stand alone appliances. Once connected to ductwork, they become a “SYSTEM”. When or if you purchase a 95+ efficiency furnace, does not mean it will deliver 95% efficiency when connected to the “SYSTEM”. Depending on how well the components are engineered and assembled will determine how efficient the system will perform. It is important to understand that the equipment ratings are only the potential of the equipment under ideal conditions.
Factors that contribute to deteriorated performance include the following:
- Builders / owners want their buildings constructed faster and at lower costs.
- Architects and consultants work with lower fees and tighter times schedules.
- Competitive pricing by the trades results in decreased installation quality.
- Shortcuts, tradeoffs and “that’s good enough” now become the focus of the installation.
With the growing complexity of the equipment and their controls, the design and installation of the system becomes critical. The equipment manuals are more detailed and the reference materials are thicker and require a higher degree of technical experience for the system to be installed and perform as the manufacture has designed it.
The National Comfort Institute has tested and balanced over 50,000 homes and businesses nationwide. It has proven documentation that the national average of installed heating and cooling systems is performing at a meager 57%. This means that barely over half the heating or cooling that your home comfort system produces is getting into the conditioned space of your home.
Sizing Matters:
Many contractors do not perform load and duct calculations. They simply size the equipment by square footage or replace the equipment with the exact size that is already there. In these cases, a load calculation has never been performed. This requirement is fairly recent.
Demand a Load Calculation – No Exceptions! After finding out what size equipment to use, never purchase the next size larger. It may sound like the load size is too small to do the job, but if the calculations were done properly; the load figure is still 20% higher than what your building requires. There is a fudge factor built into these calculations. Oversized systems never provide comfort.
Types of Heating Systems:
There are several types of systems to choose from whether they use warm air or hot water as the heated medium. These are single stage, two stage, modulating or zoned systems.
Single stage systems produce 100% of the output heat it is rated for each time it is turned on. This is the most efficient type of heating system.
Two stage systems at first produce about 50% - 60% of the output it is rated for. If additional heat is needed, the second stage allows 100% of the output to be turned on. Contrary to popular belief, the two stage system is less efficient than the single stage system. It actually uses 25% more fuel than a single stage system.
Modulating systems produce a modulating flame between 25% and 100% as determined by the space or water temperature. Contrary to popular belief, the modulation system is less efficient that the two stage system. It actually uses 33% more fuel than a single stage system.
How is this possible? Actually the size of the heat exchanger never changes. The flame inside the heat exchanger just gets smaller. This smaller flame must use more fuel to get the heat exchanger up to the correct temperature before the system will heat the building. The reason they make these choices available is they tend to keep the building at a more even space temperature.
Some homes have one furnace and air conditioner with two or more thermostats. This application is called zoning. Zoning is nice if you have a large home, a two story home or need to keep different parts of your home at different temperatures. Although zoning is an extremely nice feature to have, you need to be extra careful when choosing a HVAC contractor to install a zone system. Very few zoned systems function properly due to poor duct design and installation practices.
Duct Design:
The duct system is probably the most important part of the HVAC system, but it is also the most frequently misunderstood component. Poor duct design is the biggest contributor to breakdowns and premature equipment failure. Performing a static profile on the equipment can determine whether or not your ductwork is performing correctly. It is similar to a doctor taking your blood pressure. It allows the technician to determine if the ductwork can handle the maximum air flow required without reducing the supply fan blower performance.
Filter Sizing:
Higher efficiency filters can be a real blessing to individuals with allergies and respiratory problems. In fact, many feel this is a necessary accessory that must be added to the system. However, installing too restrictive a filter can severely deteriorate performance. Filters are usually sized so the air flowing through the filter will not diminish the supply fan blower performance. This is a very common problem found on most systems.
Ventilation Requirements:
Indoor Air Quality starts here. This is of major importance but is just as misunderstood as the duct design. With tighter built homes, the off-gassing of chemicals used in the construction of the home, radon, mold, mildew, dust, dirt, pollens, allergens and may other contaminants stay in the home and effect every breath we take. This is one of the major reasons that allergies and asthma are much more common today.
Fresh air must be brought into the home to dilute the toxic buildup of chemicals in the home. The amount of fresh air varies per home, but ASHRAE has determined that a continuous minimum of at least 45 to 95 cubic foot of air per minute is required in a standard home. Most homes are not supplied with a continuous ventilation system.
The Michigan Mechanical Code allows for natural ventilation. This refers to doors and windows that can open. It says the minimum open-able area to the outdoors shall be 4% of the floor area. So if you have a 1000 square foot home, 4 % is the same as, (1000 x .04 = 40), 40 square feet.
That would be an 8 ft x 5 ft opening, which is similar to having a sliding glass door fully open all the time. How often do you leave your sliding glass door fully open during the winter? If the answer is never, you should consider installing mechanical ventilation.
Types of Mechanical Ventilation:
There are three ways to bring in fresh outside air. One way is to run the furnace fan all the time with a 6” duct bringing in 100% outside air to the return air duct just before the air filter. You must also run at least one of the bathroom exhaust fans to provide the exchange of air. This system is the most costly to operate.
The second way is to install an HRV or Heat Recovery Unit. This system transfers the heat from the building exhaust air into the cold 100% outside air through an air to air heat exchanger. This type of system transfers sensible heat and is typically used on heating systems only.
The third way is to install an ERV or Energy Recovery Unit. This does basically the same thing as the HRV, but this system transfers both sensible heat and latent heat. This is the most efficient and is typically used when you have both heating and air conditioning installed in the home or live in a very humid area.
Additional Accessories:
The “fan-in-a-can” is an alternative that offers a way to add ventilation but it’s actually designed to replenish combustion air, (which is another topic of discussion). There are many other accessories that you can add to your system, but they are not as critical as the items we have mentioned so far. You can add humidification, ultra-violet lamps and other safeguards to the system
Test and Balance:
The products our HVAC systems deliver are all invisible. These “products” include air flow, heating, cooling, ventilation, BTU’s and finally comfort. In reality, unless these values are measured and verified, system design has not yet been proven. Often it is the measurement and adjusting that actually brings the system to the point where it functions as it should.
Independent Test and Balance companies are experts in system analysis with specialized skills and highly accurate testing equipment for discovering why systems do not perform as designed.
Heating & Cooling companies, builders, building owners, and construction teams will call on a test and balance contractor during the design phase of a project. Their experience in system analysis is helpful in locating deficiencies in the equipment selection and ductwork design.
Once a system is installed, it may be too expensive to repair (or) concealed areas that need attention are no longer accessible. When that occurs, a law firm may hire a test and balance contractor to test and verify the installation and document the deficiencies for future litigation.
If you are planning on building in the future, you may want to consider the services of a test and balance contractor. If you feel your existing system is not performing as it should, a test and balance contractor can test and verify actual performance and provide a detailed report on what steps needs to be taken to increase the performance of your equipment.
Submitted By: Lee W. Galison
Advanced HVAC Solutions, PLC
Home Builders Association - Grand Traverse Area
Green Build Committee - Grand Traverse
National Home Builders Association
ASHRAE - American Society of Heating, Refrigeration and Air-Conditioning Engineers
National Balance Institute
National Comfort Team
Reliable Controls - Factory Authorized Dealer
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