Clean and Comfortable
Creating a comfortable environment for customers is an important part of every business. Every occupied building must introduce fresh air ventilation into the space to maintain comfort for those occupants inside, and this air must be conditioned. This can be very challenging the more extreme the outside weather becomes. The ventilation air we bring into a space typically mixes with the return air already inside building as illustrated below. As a result, this changes the conditions of the supply air back to the space. To maintain the space comfort, hot air must be cooled, cold air heated, and humid air dehumidified.
External Conditions Impact on HVAC Design
The most influential outside ventilation air factor is temperature. When adapting the HVAC system in extreme heat conditions, more cooling is required. And of course, when cold conditions are a concern, the air must be heated. These environmental conditions change greatly depending on where you are in the country.
Another, often overlooked, outside air factor is humidity. When air crosses a cooling coil, condensate forms on the cooling coil, this water is drained and removed from the air stream. This process requires a great deal more energy than what is needed to cool the air. As a result, the required cooling for a space can increase significantly when outside air or space conditions have high humidity.
ASHRAE has produced the above map to show the different climate zones throughout the US. We can see as we progress further north, the temperatures grow colder. Additionally, the eastern half of the country has an overall higher humidity than the west. This means that the HVAC engineering designs need to change depending on where in the country the project is located.
One design does not fit all
When a design calls for higher outside air requirements, the demand on the conditioning equipment increases. The amount of outside air quantity is dictated by the occupancy ventilation and building air balance. If the space has a kitchen hood this will increase a buildings exhaust air and thus increases outside air requirements dramatically. These factors increase the demands on the HVAC equipment significantly.
Warmer weather means more cooling tonnage to account for the greater temperatures involved. As the outside air increases in temperature, this introduces warmer air to the HVAC system and a greater amount of cooling load to condition it. Unfortunately, the only solutions are to decrease the amount of outside air required, which may not be possible per code, or increase the HVAC tonnage.
Colder winters mean more heating for the same reasons as warm weather. While there are many ways to heat air, the two most common are through electric power or burning natural gas. In the southern portions of the country, the winters are mild and have a lower temperature change. This means that using electric heating, either a heat pump or electric resistance, can be cost effective given it also runs fewer months in the year. The further north we go, gas heating becomes far more cost effective. This is due to how great the temperature change is, as well as how the winters last much longer. Many times, the power requirement to use electric heating in the northern states becomes prohibitively expensive as it can force electric service sizes to increase. Refer to the ASHRAE heating map below.
Dehumidification Options
In addition to temperature, humidity has a large impact on the overall design. HVAC equipment can only remove so much moisture from the air, some will get through. While completely dry air can be uncomfortable, so can humid air. Any additional moisture that gets into the space will remain until it is removed. If the HVAC system is constantly adding humid outside air, removing that space moisture becomes increasingly difficult. Dehumidification options for air conditioning systems allows for an extra step in the cooling process that removes additional moisture from the air. This helps to ensure that the occupied space maintains not only the temperatures desired, but the humidity.
Do not worry, Interplan can help!
As we have discussed in this post, one design does not fit all. Outside air temperature, humidity and ventilation requirements all play a role in the design of the HVAC system. Interplan counts with a number of experienced HVAC engineers with extensive experience design systems nationwide who can help make sure your HVAC system is designed to meet all the specific requirements to keep your space functional and comfortable.
For more information, reach out to Interplan LLC: (407)645-5008
