HVAC Equipment Installation:
Heating & Cooling Performance Issues
Improving heating & cooling efficiency and effectiveness is a home performance goal. Depending on homeowner flexibility and budget, it can be achieved in variety of ways.
Total system replacement and redesign combined with insulation and window improvement leads to maximum results, but it comes at high price. However, better results are possible for everyone.
Discussions in this article include:
- Current State of Heating & Cooling System Installation
- Contributing Issues to Under-Performing Systems
- Diagnosing Heating & Cooling System Installation
- Selecting Heating & Cooling System Options
- Central Heating & Cooling Performance Factors
- Customer Performance Targets
- Improving Heating & Cooling System Performance
This article focuses on central heating & cooling systems. Similar principles and processes apply to other types of heating & cooling systems. Other types are not discussed here, but most are evaluated as part a home energy audit.
Note: Window air conditioners and evaporative coolers are not evaluated as part of home energy audit.
Current State of Heating & Cooling System Installation
Equipment tends to be twice as large or more than it needs to be. Also, Many systems are at least partially installed in hostile environment because of temperature extremes or high moisture content
Contributing Issues to Under-Performing Systems
This state of affairs exists because rules of thumb, rather than engineering design, used to install system components. To make matters worse, customer complaints are “resolved” installing bigger equipment, rather than by replanning.
The broad category most HVAC contractors start with is equipment size. It’s the wrong place to start, but it’s the easiest one to understand.
The first system is installed using rules of thumb, not building performance characteristics. When the original system doesn’t make to occupants happy, the response is bigger is better. Fixing the real problems are too time consuming and the cut into profit margins.
The architect doesn’t help matters. They assume the HVAC contractor will make due with whatever building structure is given to them.
There is no real up-front planning. When equipment is replaced, typically the assumption is made that what was installed before was okay—only an equipment change is needed. And we let them get away with it because we trust them. What other choice do we have?
Home Energy Audit: Diagnosing Heating & Cooling Equipment
Tip: Diagnosing central heating & cooling system depend on central heating & cooling performance factors.
The process for improving heating & cooling performance follows this path:
- Interview Homeowners
- Evaluate Existing Heating & Cooling Systems
- Pick Equipment or System Improvement Options
- Prepare Heating & Cooling Systems
- Commission (Performance Tune) Systems
- Check Comfort Performance
Interview Homeowners. Improving home performance is about providing a healthier, longer lasting, more comfortable, and energy efficient house.
As they relate to heating & cooling, the following questions are asked during the homeowner interview
How often do you need to dust?
Who in your family has allergies?
Who in your family has asthma?
When was the equipment installed?
Why was the equipment replaced?
What is the maintenance history?
Are there any hot or cold rooms?
Does moisture condense on the windows?
When system is running, what kind of noises does it make?
From your perspective: energy bills high, low, or average?
Is there anything else you feel is relevant?
Answers to these questions help us evaluate the system in terms of moisture control, indoor air quality, and energy transfer: the golden home performance triangle.
Visual Assessment. Before modifying or adding heating & cooling systems, the heat-load characteristics need to be known. This includes where and how much insulation is installed, types of windows in place, and the direction the front of the house faces.
Installation & Operational Checks. The equipment and ductwork need to be looked at for proper installation, as well as find out whether the system passes basic heating and cooling checks.
Define Existing System. For analysis, the conditioned floor area for each system and the volume of the house has to be known. To begin working with the HVAC contractors, we need to provide them with a map of the house, showing room size, supply register locations and sizes, and return air pathways.
Diagnostic Testing. The amount of heating and cooling required is a function of heat loss, including what is lost through holes in the building and ductwork.
To get a sense of what is happening now, air infiltration, duct leakage, and pressure balance measurements are made.
For safety reasons, anytime there are fireplaces or fossil fuel water heaters or furnaces present, depressurization checks are needed under various fan conditions and door states (open or closed) to determine whether backdrafting smoke back into the house is a possibility.
System Analysis. After the day is done evaluating the house, the results are analyzed to establish system improvement priorities. The priorities are used to develop recommendations and the scope of work.
After the homeowner interview, a visual assessment of the heating & cooling system is made, followed by diagnostic testing. The results are analyzed to prioritize recommendations.
Pick Improvement Options. During the homeowner interview, the process was started to begin establishing the expectations and goals of the improved heating & cooling system. It’s not always possible, but an initial attempt is made to make recommendations based on equipment/ductwork option chosen during the interview.
Scoping the Work. As recommendations, options, and price ranges are presented, other equipment/ductwork options may emerge. This process may iterate several times before the final home performance solution is chosen.
Setting Expectations. Every homeowner has expectations and unstated goals for their heating & cooling system. At the beginning of the process, homeowners may not have thought about their improved systems in these terms.
Every homeowner needs understand the range of possibilities to begin to make informed choices. The process we follow is iterative, so everyone has a clear understanding what to achieve by the end of the project.
Requirements. During this interview, we all start to get a sense for what the homeowner wants by exploring the replacement options for equipment and ductwork. Part of the process is understanding what else homeowners want because it directly impacts recommendations for the heating & cooling system.
Impact of Other Decisions. Air sealing walls, windows, and floors; adding insulation, and replacing windows has a direct impact on reducing the size of the system to be installed. Any possible changes to the size of conditioned spaces needs to be known before beginning to plan flexibility into the system.
Selecting Heating & Cooling System Options. There are four options for improving central heating & cooling systems.
New Equipment, New Ductwork. When there is a willingness to do whatever it takes to maximize heating and cooling system efficiency and effectiveness while minimizing operating costs, home performance savvy HVAC contractors have the greatest range of options for delivering it.
Design System First. To accomplish this, the house’s heat load characteristics needs to be modeled and the entire heating & cooling system designed to engineer standards. This approach costs the most and may not be easily feasible.
Whatever option is chosen, the ductwork needs to be sealed. There is a variety of duct sealing methods available.
New Equipment, Same Ducts. When using new equipment with the same ducts, the desire is try to use the existing ductwork, if possible. Ductwork may be hard to get to without extensive remodeling. Also, the may be a desire not to plug abandoned holes in the walls, ceilings, or floors when the duct registers are relocated.
Match Equipment to Ductwork. In this approach, equipment needs to be chosen that can be made to fit the ductwork while operating the way the manufacturer intended. To accomplish this, the house’s heat load characteristics needs to be modeled.
Same Equipment, New Ducts. When the same equipment / new ducts option is selected, the equipment may be new, but the job wasn’t finished when it was installed. There are a lot of efficiencies that can be gained designing the air distribution system.
Redesign Ductwork. To ensure proper equipment performance, the ductwork must match the equipment. To accomplish this, the house’s heat load characteristics needs to be modeled. Before performance tuning the system, the filters and coils need to be cleaned.
Same Equipment, Same Ducts. The least preferred option is using the same equipment and ductwork, in most cases. Assuming the equipment and ductwork are reasonably matched and is appropriate for the house, this can be the least-cost option, but also has the least amount of flexibility.
Smaller performance efficiencies are also more likely than any other option. However, it’s a great place to start while implementing other home performance improvements over time.
Pre-Cleaning Required. To accomplish this, the house’s heat load characteristics should be modeled to allow for better decision making. Before performance tuning the system, the filters and coils need to be cleaned.