HVAC Equipment Installation:
Heating & Cooling Performance Improvement
HVAC professionals have got it right, the heating & cooling system is the comfort system. Getting this system right depends on what is done with the rest of the house.
Better systems result from other home performance improvements completed first, such as air sealing, improving the thermal barrier, modifying windows, and controlling ventilation.
When the project is complete, ideally these customer system design requirements should be met.
Indoor air temps within 3-5º F, floor-ceiling, even in multi-story houses
Indoor air temperatures stay within 3 degrees of the thermostat set point
System sealed & separate from outside
Depending on the area of the country, 10-25¢ per ft2 of heated floor area per year for heating & cooling costs at 70º Fahrenheit is possible for those willing to do what it takes to improve the heat-load characteristics of the house while installing efficient systems.
Prepare Heating & Cooling System
Correct Home Performance Issues. After the home energy audit, several whole-house improvement options may have been explored. Several proposed improvements need to be made before or during the improvement of the heating & cooling system.
System Preparation. Once work begins on the heating & cooling system itself, the first step is to put the components of the system together after designing the system. Every effort should be made meet room and system airflow needs after sealing the ductwork.
If existing equipment is used, the filters and coils need to be cleaned before performance tuning the system.
Commission (Performance Tune) System
To startup the system, six steps are followed—all technical in nature.
Tune System Airflow. The first step is ensuring system airflow is adequate. If not, obvious things must be looked for and addressed, such as adjusting fan speed, fixing broken ductwork, or correcting duct size or type.
After taking care of obvious things, static pressure is measured at the indoor equipment (air handler unit). When pressure is too high, return air paths may need to be corrected, registers added, duct sizes increased, or any of these in combination.
Minimize Duct Leakage. During the installation process, the first attempt to seal the ductwork was made. It’s done to make a reasonable attempt to get the system airflow right. The next step is to measure how leaky the air distribution system is to further seal the ductwork, as appropriate.
There is no real standard established for sealing ductwork. However, various home performance programs do set their own targets. The sponsor for incentive programs dictates with the performance improvement for duct leakage has to be to qualify.
Insulate Ductwork. Major system improvement gains are possible by insulating ductwork. The building code standard is too low and leads to unnecessary heat loss.
In our opinion, where possible, insulation around ductwork needs to match insulation requirements for the area it’s running through. For instance, R-30 in an attic and R-19 under a floor in an unconditioned basement or crawlspace. Insulation is not required in conditioned areas, but R-6 helps, especially in humid areas.
Adjust Refrigerant. Proper refrigerant charge is measured to the ounce, so it’s pretty precise. Assuming the lineset between equipment is installed properly and there are no leaks, the system can be filled with refrigerant.
On new systems, a thermostatic expansion valve (TXV) should be installed to regulate refrigerant flow under varying temperature conditions. When used, the charge needs to be tested using both the Sub-Cool and Super-Heat methods.
Measure Room Airflows. The moment of truth comes when room airflows are measured. At a minimum, the volume of air delivered to the room should be within 10% of the design (from the Manual J Report).
There are other concerns for room airflow, such as air mixing. Room air delivery is a function of velocity, direction, and volume. Measuring room airflows determines volume only. For better performance and comfort, registers and grilles need to match the room and ductwork. The registers need to be positioned for maximum air mixing. See Central Heating & Cooling System Performance Factors for more information.
If balancing room airflows is not possible with dampers, the ductwork will have to be adjusted, and the performance tuning process started again.
Balance Room Airflows. The final performance tuning step is balancing airflow to each room using dampers set close to plenums (e.g., plenums, trunklines, distribution boxes) rather than by registers. Doing so reduces noise, uses available air better, and prolongs equipment life.
Check Comfort Performance
Performance Guarantees. Following these steps for improving heating & cooling performance does not guarantee customer design targets are met, but they will be significantly better! The risk that they don’t increases as design options for the HVAC contractor are minimized.
Better Performance Delivered. Following this process improves system performance, leading to a healthier, longer lasting, and more energy efficient house. Comfort also improves to some degree. However, getting the air to mix right is key to getting the system to operate within the desired comfort ranges.
Post System Installation Testing
When the contractor is done final testing is needed, sometimes by a third-party who didn’t do the work.
For home performance contractors, final testing is mandatory when there are combustion appliances are present. The concern is ensuring the areas fire places, water heaters, and furnaces are in are not depressurized to the point of causing smoke to backdraft into the house.
Where there are incentives or certificates offered, the sponsor usually requires final testing too. Their considerations are to verify better equipment was installed, duct leakage meets or exceeds performance targets, or system performance is improved.
We are ready, willing, and able to perform third-party testing.
Here’s to a better heating & cooling system!