I want to address a topic that comes up in every programming interview that very few people give much thought to…Indoor heating and air conditioning…
The professional term HVAC stands for Heating, Ventilation, Air Conditioning and pretty much sums up your indoor air climate. For those of us in the higher elevations of a more northerly lattitude, heating is a significant concern and few have A/C where in the southern lattitudes, homes may focus more on A/C and rarely concern themselves with heat. And everyone should concern themselves with ventilation in their building whether it is done naturally with careful window placement and operation, or mechanically with blowers and filters. This blog will concern itself primarily with residential home HVAC and commercial systems shall be another post some other time.
There are two primary mediums in which one may transfer heat in their home. Moving air and moving water. Neither of these seems terribly high tech, and when you get right down to it, modern home heating systems fundamentally haven’t changed much for quite some time. While advances in effeciencies have been tremendous, the core technology of heating air or water and moving it is still the same.
GFA ($): This means a Gas Forced Air system. Quite simple really – you have a furnace which burns fuel or has an electric heating element that warms air in a heat exchange chamber. Then a fan blows the heated air from the chamber through supply ducts to different portions of the home. A return duct sucks the air back into the chamber and the process continues in a loop. When you want air conditioning in the summertime, the same system exhanges the heat from the chamber to a separate refrigerant loop which takes the heat outside and effectively cools the air in the chamber, then the blower system circulates the cool air. Moving air tends to be an uncomfortable way to heat a home as it can be loud and can cause drafts, however it is one of the less expensive methods.
High Speed Air ($$): Same basic idea, but the air moves much faster through smaller ducts. Great for remodels where you don’t have the luxury of space to run ductwork. Manufacturers claim that sound is less of an issue because of duct size and other design features
Electric baseboard ($): cheap to install, but expensive to operate, these registers simply heat with an electrical element (like in a stove) and exchange heat directly with the surrounding air in a baseboard type unit. No A/C possible with electric systems.
In-floor electric radiant ($$$): this is an electric resistance mat installed under a tile floor. very expensive to install and to run, but might be appropriate for very small areas like just a master bathroom if you seek warm toes on a winter morning.
The next systems are Hydronic systems. “Hydronic” is just a fancy word that simply means water. Water can be used any number of ways…
Hot Water Baseboard ($$): The simplest is to have a boiler heat the water (again, burning fuel or using an electric element). Then the water is circulated with a small pump to various locations within the home that have a radiator of some kind. In much older homes, the radiators are quite large and take up quite a bit of space, but since the 60’s, radiators have been replaced with baseboard heating registers. Still radiators, but much smaller and lower profile. Air conditioning is generally not supported in a system like this because of convective challenges in the baseboards.
In-Floor Radiant ($$$): Water can also be circulated in the floor of the home. This can be done with the piping that circulates the water embedded in a concrete slab, a lightweight gyp-crete slab on a structural wood floor deck, or stapled up under the plywood floor (staple-up). There are other products out there for in-floor radiant, but they all function essentially the same. Part of the cost of a system like this is in the structure that supports the additional mass. This is an extremely comfortable way to heat a home, but it does not support A/C very well and the response time for a temperature change is very slow. It can also wreak havoc on some hardwood floors, so be careful here.
In-wall radiant ($$$?): Same basic idea as in-floor, but the pipes run in concrete walls. This system obviously requires much more planning and concrete exterior walls, but we’ve seen it and it appears to be very effective.
Fan Coil ($$): This system still has the boiler, but it moves water throughout the house to a small exchanger that has a fan attached to it that will blow the hot or cold air at the point of exchange. The nice thing here is a rapid response to temperature change.
Hybrid systems ($$-$$$): These systems are composite systems, like in-floor radiant in a lower level slab, but fan coil heat in upper levels of the home. These methods can be very effective to customize the type of heat and A/C in a home.
And let’s not forget the good old fireplace. Some may argue that a traditional fireplace is actually an A/C topic and not a heating device because of its abysmal efficiency and ability to draw cold air into a space. We highly recommend inserts, stoves, gas units, anything that can contain the movement of air and maximize the BTUs available in the fuel. Sometimes, we use these as the sole heating source for cabins or weekend places. The traditional open hearth fireplace looks nice, but forget about relying on it solely for heat.
So that’s the basic rundown for most of the options available for central HVAC in a home. Every home is different and everyone has different preferences and different budgets. It is a very important element in the design of your home, and something we tend to talk a lot about because it can really affect the life-cycle cost of the home as energy prices go up. We also like to talk about it very early on in the programming phase as it can quickly drive a myriad of other design decisions.