Now that we’ve reduced the heating requirements of Geos homes by 80% and the cooling requirements to almost nothing, we needed to find the optimal system for providing heat on cloudy winter days and cold nights. The peak heating requirements (loads) for most Geos homes are 1/4 the capacity of the smallest furnace available on the market. One astounding fact about traditional HVAC systems is that they’re sized to produce enough heat to keep the home at 70 degrees on the coldest night — 0ºF to -10ºF in Denver, but for 80% of the hours in a year where heat is needed, they need 1/3 of that capacity. Therefore, 2/3’s of the cost of the heating system is only used 20% of the time.
At Geos, we have completely re-engineered how we heat homes. If our peak heating load is already 1/4 the size of the smallest furnace, we knew we would be wasting money if we didn’t think of something different. And when we ran our computer modeling on these extremely efficient homes, we found out that 80% of the time, the heating requirements were only 6,000 Btus. So what does that mean?
Conveniently, the mechanical ventilation system that is required to provide sufficient fresh air to the home requires 3” duct work. That’s the perfect size for running ducts within the interior walls of the home. What’s also great about 3” duct work? It’s exactly the size duct work necessary to deliver 6,000 Btus of heat. This means that for 80% of the time, our homes need zero additional duct work — no drop soffits, no chases, no unsightly drywall surrounds, and it costs much less
to not have to run large ducts throughout the house.
So where does that 6,000 Btus of heat come from? Currently, we have a couple of different options. One scenario would use a single ground source heat pump (sometimes referred to as Geothermal) to push heat through multiple connected buildings and into a small fan coil between the ERV and the ventilation ducts. The other option is to install a mini-split air source heat pump system with a ducted head between the ERV and the ventilation ducts. Modern mini split systems can be extremely energy efficient and are variable speed, so they only deliver the amount of heat necessary to maintain comfort. And since we are integrating with the ventilation system, there are no separate room units to distract from the decor.
Ok, now how do we deliver the rest of the heat on the really cold days? Traditional electric strip heaters! We only need one small unit on each floor to produce all the extra heat that’s necessary. Electric resistance heat uses a lot of electricity, but if it’s only being used 20% of the total heating hours in the year, all it takes is one extra solar PV panel to make up the difference! That’s a substantial cost savings that we can pass on to you.
For the larger homes, the heating loads are large enough that we can utilize the smallest ground source heat pump available from Bosch. These are two stage units, meaning they can run at 1/2 capacity for most of the time and and full capacity on the coldest nights.