Almost a year ago we began planning the HVAC system in our new office and had to decide what we wanted to do. We knew we didn't want to do the "normal" of a forced air heating and air system as that is what we were coming from and recognize the shortcomings of that system. Even with a heat pump and zoning we found ourselves constantly fighting the temperature in the office and it was not particularly efficient overall. We also didn't have an unlimited budget, so we had to balance comfort, efficiency, Indoor air quality and price.
In the end we decided on radiant heat in the concrete slab floor of the offices, a hanging heater for the warehouse area (to keep it above freezing mostly), and mini-split heat pumps in every office space. If a customer wanted to have the best comfort and efficiency, this is the direction we would point them as well.
Radiant tubing attached to the grid before the floor is poured
The radiant floor heat will provide a very even baseline temperature throughout the office (and keep our toes warm). The thermostat controlling the system has a floor temperature sensor and an air temperature sensor to make sure we're keeping the slab warm without overheating the air above it and making sure the floor maintains at least a minimum temperature throughout the heating season.
The mini-splits are part of a heat pump system, which means they can both heat and cool the space they are in. In the cooling months, they provide precise, quiet, and efficient cooling to each area. That means that when Tom wants his office 65 degrees he can do that without making everyone else cold. When Pat doesn't want any cooling in her office, she can do that too. In the winter, we have the heated floors providing a baseline temperature for the entire office while the ductless units take care of fine-tuning the temperature in every room above the heat the floors provide.
The Ductless heads blend in nicely with their surroundings
Every single space having its own temperature control takes a little getting used to. Just like you would turn a light off when you leave a room you don't intend to come back to or aren't using we try to simply turn the system off when we leave for the day or in the case of a conference room on turn the system on only when it is used. Between the super insulated and air sealed exterior and the quick recovery of the system the room can be made comfortable in matter of minutes. After a few months it looks like the new building will cost the same or less than the old building that was one third the size.
Speaking of the building, lets talk about its role keeping us comfortable and minimizing the monthly energy bills. The building is a pole framed building over an insulated concrete slab. The exterior walls and the underside of the roof deck were sprayed with at least 6 inches of open cell foam insulation. When combined with the steel siding and roof and the house wrap below it, things are very tight from an air leakage perspective.
With that tightness in mind we wanted to make sure we didn't forget the "V" in HVAC - ventilation. The last thing we want is a temperature controlled Petri dish - we want to make sure we have a way to bring in fresh air and exhaust the stale. To that end, we have an Energy Recovery Ventilator. This unit takes in air from one end of the building, exhausts it outside and brings in fresh outside air to the other side of the building. This isn't just like opening a window, however. Both air streams pass through something called an enthalpy core where they exchange their heat and humidity. That means that in the hot summer we don't just send out nice cool and dehumified air and bring in hot humid air. Instead, the ERV moves most of the heat and humidity from the incoming air into the air leaving the building. That way we get the best of both worlds - fresh air and energy savings vs. just bringing in outside air unconditioned and "throwing out" nicely conditioned air.
The inside of the ERV
Overall we've been very happy with the system and being able to set your own temperature is a nice luxury to have. We'll see what the cold weather brings, but we have every reason to believe the choices we've made will allow us many years of trouble free comfort. Check out the gallery below for even more pictures.