By Dan Copeland, JEA Customer Solutions Field Representative
The topic of comfort arises quite frequently when speaking to people about their homes.
When people are uncomfortable in their home, they generally are not shy about telling someone else about it. Spouses and family members fight over thermostat settings trying to achieve it.
Homeowners spend money on HVAC, insulation, curtains, space heaters and fans to try to improve it. But what exactly is it?
Without a doubt comfort is subjective. What one person finds comfortable another may not. There are a number of factors contributing to comfort including air temperature, humidity, radiant temperatures, air flow and clothing.
Think about it: If we were outside on one of Jacksonville’s cold January mornings and one of us was wearing a swim suit while the other was wearing pants and a jacket, we would give different answers as to status of our comfort.
Since we rely so much on our HVAC systems for comfort in Jacksonville, we’ll discuss comfort and best practices for installing HVAC systems to ensure comfort afterwards.
The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) provided a range of what is acceptable to 80 percent of people in ASHRAE Standard 55.
To put that information into context of a residential home the Air Conditioning Contractors of America (ACCA) created the ACCA Manual RS. Manual RS covers system design, equipment selection, zoning and more.
There is a particularly useful table that can be used to define comfort in a residential building. ACCA calls this the “Minimum/Maximum Recommended Values for Comfort and Safety.” This table will provide what is reasonably achievable with modern buildings and HVAC equipment.
In summary, the highlights are as follows: thermostat set point 75 degrees, relative humidity 55 percent max, room-to-room temp splits 6 degrees, floor-to-floor temp splits 6 degrees max, air temp split from thermostat set point 3 degrees. (For the technical details, check out ACCA Manual RS.)
Now that we have a framework to define comfort, the next big question is how do we achieve it?
Many of the same steps should be taken in both new construction and an HVAC retrofit. Some of them are required in new construction but not so much in system swap-outs. Taking these steps in any situation will help ensure a higher likelihood of the end-user being happy and comfortable when it’s all said and done.
First things first: evaluate the existing home or set of plans. This is especially important for existing homes. Over the years, homes change. Additions are built, windows replaced, insulation added and ductwork gets crushed.
If a duct system is in poor shape, there are large air leaks to unconditioned space, or there is little insulation, then substantial impacts on comfort will result. Budgeting for and correcting them first will do wonders for making it more cost-effective to achieve comfort in a home with HVAC.
Next, have a Manual J (system sizing) calculation completed based on actual or planned values. Better yet, spend a few more moments and complete a room-by-room Manual J calculation. Then verify that the equipment that is going to be installed matches what is called for from Manual J.
For new construction spending the time to do a proper duct design based on Manual D will also yield better comfort results in the end.
Once the HVAC equipment is installed, the last step is to verify its performance. By measuring the total external static pressure, air flow from each duct run and temperatures of air entering and exiting the system, then the delivered performance of the system can be calculated.
Low performance may indicate duct restrictions, incorrect system charge and more. If needed, adjustments can then be made to balance the system to ensure that each room gets the needed air flow as determined by the Manual J calculation.
If duct repairs were made in an existing home, conducting a duct leakage test is a good idea as well to verify that the conditioned air is actually making it into conditioned space and not the attic. On an HVAC retrofit simply swapping the boxes is no guarantee of comfort for the customer.
In new construction simply selecting high-efficiency equipment is no guarantee either. Taking the time to properly evaluate the needs of a home, design the ductwork, install the equipment, and then the performance will ensure that end-users are comfortable in their homes