Staying comfortable in the summers of Montana many times requires some variation of a mechanical cooling system. Most folks agree, the number of days where it is uncomfortable is limited in our state. There are exceptions to this, and that is primarily due to solar gain issues that southern and western windows imposed on a home or business. There are certainly internal heat gains in most commercial establishments that require cooling or the customers find a more comfortable place to shop. The following methods of cooling are the most common applications that we see.
Ducted cooling systems have been around for some 50-60 years now and are a mainstay of life in hotter and more humid areas of the country. As much as I love boiler and radiant heating systems, they don’t have the distribution necessary to provide cooling. This is one of the major selling points of a gas furnace systems, is their ability to easily add cooling. Most modern furnaces (under 18-20 years old) are designed to allow addition of a cooling coil on the outlet side of the machine. The blower needs to have the capacity to overcome the restriction of the A/C coil and the control system needs to be wired with A/C in mind. The ducting often times is compatible, but having cooling in mind when the system is designed will make the system perform much better. Things such as; properly sized ducting, high wall returns, ample outlets, properly positioned outlets, and enough room to physically add an A/C coil on the outlet of the furnace.
There are two basic components; the outdoor condenser and the indoor evaporator coil. There are refrigeration lines that connect the two components and control wiring and line voltage power wiring. We are simply removing heat from the home (makes it cooler) and rejecting that heat outside through the condenser. A very popular design does not need a furnace, it relies on an “air handler” to move the air through the ducting. It is similar in size to a furnace but includes only the A/C evaporator coil and the blower system. A variety of options are available in both air handlers and outside condensers that affect efficiency of the system, reliability, and noise levels. Fortunately in Montana, because of the short cooling season, your A/C unit will last a very long time (choose wisely).
These systems are also covered in the heat pump section because they generally do both heating and cooling. The ductless revolution is in full swing and they certainly are well suited for cooling, often better than a central system. Because our cooling load is mainly solar gain, that extreme temperature is limited to certain areas of the home. That heat obviously carries throughout the upper levels of the home but it usually starts with one area. Installing a ductless system in this area will squelch this heat build-up and make the entire home more comfortable. Often times this is a wall of glass that makes positioning enough cooling from a ducted system impossible. You can apply a large amount of cooling in a small physical space with the ductless design.
Another major advantage over a ducted system is the problem with cooling a multilevel home. Putting cooling on the entire home through a duct system will cool the already cool basement to a refrigerated state. The upper floor is usually not ducted as well, and it doesn’t receive enough cooling. The main level where the thermostat is, remains comfortable, everywhere else is a compromise.
As with the heat pumps, multiple indoor units can run off of a single outdoor unit, saving money and simplifying the system.
Package units are designed to be the most heating and cooling for the money. They are on rooftops all over the world and have been keeping you comfortable during most of your shopping adventures. Being one single piece of equipment, they are assembled at the factory and ready to run shortly after being set on the pad. Since most commercial applications require fresh air to be introduced, outside air dampers are a standard feature. Unfortunitly they are not particularly efficient. The combustion efficiency is limited to 80% which is the minimum that the DOE allows. The cooling efficiency of these units is getting better but the desire to make the units physically smaller limits the coil surface area and thus the efficiency. They are very versatile in that they are produced from a tiny 24,000 BTUH unit up to 100’s of thousands of BTUH’s. Package units are available in gas or heat pump versions depending on your application.