Top 10 A/C Issue Affecting Performance
- Leakage on the return (intake) side ducts
- Leakage on the supply (exhaust) side ducts
- Undersized return side duct work
- Restrictive register & return grill
- Duct layout & installation
- Un-insulated duct work
- Improper refrigerant charge
- Improper equipment sizing
- Improper equipment match
- Improper equipment maintenance
Many people know that SEER or Seasonal Energy Efficiency Ratio is a measurement of the efficiency of heating and air conditioning equipment. What most people don’t realize is that the HVAC contractor has a major role in making equipment perform up to its real capacity. Studies have shown that 12 SEER equipment installed incorrectly can perform no better than 6 SEER equipment. Needless to say, homeowners are not happy when they purchase a new piece of equipment and they do not receive the performance benefits anticipated.
Attached is a list of factors which impact a new or older air conditioning or heating system. The four main components are:
- Duct Leakage
- Air Flow
- Duct Insulation
- Refrigerant Charge
- Equipment selection
- Improper maintenance
1. Leakage on the return (intake) side ducts
93% of field tested and newly installed systems had duct leakage which reduced system performance.
A properly sealed and insulated duct system can make your home more comfortable, energy efficient and safer. Sealed ducts represent one of the best improvements for better air flow and air contaminates infiltrations.
Return side duct leakage occurs at the unit connections, seams, boot boxes and return grill locations. Return side leakage typically occurs after the filter and can have a more substantial impact on a systems performance than on the supply side.
Leaky ducts in attic spaces 140 – 150 degree attic air and blend the air with conditioned space air. The result is higher duct air temperature when the air reaches the coils. Attic air which is sucked into the duct system also coats coils and blower wheels with dust and debris further reducing the efficiency.
2. Leakage on the supply (exhaust) side ducts
Supply side leakage is easy to understand. You are paying to condition the air and losing a percentage of the air intended for the living space will reduce flow, increase run times and degrade performance. Supply side leakage actually reduces the cooling or heating capacity of a system.
3. Undersized duct work
70% of field tested, newly installed systems had air flow issues which reduced system performance.
Without proper air flow, heating and air conditioning systems lose capacity and performance. Air flow restrictions occur in a number of locations and are often times caused by poor design or construction practices.
Poor duct design causes an inadequate amount of air flow. It is very common on the return (intake) side which causes air starved units. Static pressure tests and best practices charts identify undersized duct work.
4. Restrictive register & return grills
Improper air filtration is a very common problem in many homes. It is more than just changing the filters regularly all though that is very important. Air filters and filter grills service more than one function. Their job is not only to take the particulates out of the air but to do it while not restricting air flow. This is not a simple task as the two work against each other in most case. In order to accomplish these task affectively, a properly sized grill and good quality filter need to be coupled and maintained. Don’t be surprised if your home has an undersized return grill and your air conditioning or heating system is being starved for air.
You can perform a simple assessment of your home by reviewing the chart below and comparing it to your system.
|Tonnage||CFM Rate||Duct Size||Bar- Faced*||Stamp Faced*|
|* Based on the ACCA Standards and Filter Manufactures Standards|
|** Square inches of grill space|
5. Duct Layout & Installation
Long duct runs, kinked or improperly hung duct work will reduce a piece of duct works air flow capacity.
6. Un-Insulated Duct Work
Air conditioning and heating systems use forced air ducts to distribute conditioned air throughout the home. When air conditioning ducts are not insulated properly, this causes the system to not achieve the temperature change in the air it is attempting to condition. The air conditioning or heating system effectively cannot perform its job correctly and systems run longer, are more likely to breakdown and their life expectancy is shortened.
7. Improper Refrigerant Charge
70% of field tested, newly installed systems had refrigerant charge which reduced system performance.
Getting the right refrigerant charge is a critical field adjustment factor that is often overlooked. Even a minor over or under charged system can reduce performance by as much as 20%. A field study showed that 7 out of 10 homes are improperly charged with most systems operating with less refrigerant than manufacture recommendations.
8. Improper equipment sizing
The proper size for equipment is really a matter of definition. Equipment that is “too big” will keep people comfortable when there is a large cooling demand, but it will hurt performance and be a burden the rest of the time. Often times, equipment that is “too small” will not satisfy the cooling needs. According to American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) recommendations, a system should be designed so that it runs full time for 2.5% of the summer season.
Builders and contractors often oversize because they think it will reduce service calls. Field studies show that central air conditioners are, on average, being oversized from 24% to over 100%. Graph 4 shows how reduction in efficiency caused by oversizing can reduce the performance of air-conditioning equipment. Oversizing has a bad effect on energy use, comfort, equipment life, and system costs:
- Oversized equipment often runs for very short periods and often may not reach its steady state “cruising speed” where it operates most efficiently. Oversizing by 50% has been shown to increase seasonal energy use by 9%.
- Very short runtimes mean indoor air doesn’t get mixed, and uncomfortable “hot spots” occur in kitchens and sunny rooms.
- Very short runtimes can leave too much uncomfortable humidity in the air.
- Comfort problems lead homeowners to lower the thermostat, leading to unnecessary energy use and increasing the risk of condensation problems.
- Homeowners spend more time on the outside fringes of the comfort zone and often reset the thermostat.
- Wear and tear on equipment results from too-frequent stopping and starting.
- Costs of equipment, installation, and maintenance are
9. Improper Equipment Maintenance
Just like you wouldn’t drive your car without getting the oil changed or replacing the tires when they are wore out, you should operate your mechanical system without proper maintenance. Everyone knows that pay a little now on maintenance or spend a lot later.
Many air conditioning contractors offer inexpensive “Loss Leader” checkup services that offer little or no maintenance services. A proper season maintenance program will lubricate moving parts, tighten components, adjust and calibrate components and clean the system. REEIS offers a multiple maintenance services. Click on this link to learn more.
10. Improper Homeowner Maintenance
Improper air filtration is a very common problem in many homes. It is more than just changing the filters regularly all though that is very important. Air filters and filter grills service more than one function. Their job is not only to take the particulates out of the air but to do it while not restricting air flow.
REEIS sells high quality air filters which can be installed at the time of maintenance or ordered and delivered to your home.