Importance of Climate Zones in the USA | HVAC design aspects

There are many technologies that improve the performance of HVAC systems in buildings, allowing a drastic reduction in electricity and gas bills. However, these measures may become useless under certain weather conditions. For example, a high-efficiency boiler can offer attractive savings in the Northeastern US, where winters are cold and heating bills are high. However, these boilers are of no use in tropical locations, where buildings do not even have space heating in many cases.

In general, you should stay away from “revenue-based updates” for your building systems. Avoid purchasing equipment just because you saw advertising offering an attractive energy saving percentage. Only an energy audit can provide a reasonable estimate of the performance of different building improvements.

Get an HVAC design that meets your building's unique needs.

Performance of building upgrades in different climates

New York, New Jersey and many other places in the US have a cooling season and a heating season, but there are also important differences even between places that require both cooling and heating for buildings. If a given climate requires many days of cooling and only a few days of heating, homeowners benefit from prioritizing air conditioning upgrades, while the opposite applies in places where winter is more intense than summer.

Some improvements to existing HVAC systems are also weather dependent. For example, air conditioning economizers and energy recovery ventilation (ERV) are only effective under some weather conditions. If the local climate offers few or no opportunities to use these devices, their initial cost is difficult to justify.

Local climate also influences the effectiveness of solar panels and wind turbines. However, note that these technologies may be viable even in locations with moderate wind or sun. As an example, consider the following two solar energy systems:

• System #1: 10 kW, generates 12,000 kWh/year in a building paying 25 cents/kWh.
• System #2: 10 kW, generates 16,000 kWh/year in a building paying 12.5 cents/kWh.

In this case, the second solar energy system is more productive, but the first is more profitable. Although the first system only produces 75% as much energy as the second, it saves $3,000/year, while the second only saves $2,000/year.

Overview of Climate Zones in North America

The U.S. Department of Energy provides a compact and informative list of climate zones in North America and what to expect in terms of heating and cooling loads. The local climate is one of the most important aspects considered by energy consultants and HVAC designers before carrying out energy modeling for your building.

Before proceeding with the definition of climate zones, it is important to understand the concepts of heating degree days (HDD) and cooling degree days (CDD).

• The concept of HDD refers to temperature differences below a specified value, typically 65°F. For example, a day at 60°F adds 5 HDD and a day at 55°F adds 10 HDD. Repeat the procedure throughout the year and you will get the annual HDD.
• CDD is the same concept applied to cooling: daily temperature differences above a specified value. A day at 70°F adds 5 CDD and a day at 75°F adds 10 CDD.

In general, climate types are described in terms of temperature and precipitation. These are among the main variables that must be controlled by indoor HVAC systems, maintaining the supply of fresh air and extracting air that accumulates pollutants.

As you can see from the table above, weather conditions are extremely varied and HVAC design requirements are affected accordingly. You will achieve the best results with building-specific solutions, considering both the climate and building codes applicable in your location.