Heating and cooling system
return to As Built
We have designed a system for heating and cooling that integrates passive and highly efficient active systems to create an ultra-efficient and healthy HVAC system for a building. The rationale for a hybrid type system is to allow the earth's natural systems (e.g. the sun and earth) to do as much of the heating and cooling work as possible, and only when they cannot meet the required heating and cooling levels are high-efficiency mechanical systems required to complete the job.
Strategy for our hybrid heating and cooling system
- Reduce the demand for heating and cooling by utilizing passive design ideas, such as super insulation (see Super Insulated Building Envelope), natural lighting, highly efficient windows, and a tight building envelope.
- Use solar thermal panels to heat water that is stored in 2 stainless-steel insulated tanks (totaling 5,000 gallons). That water is pumped through a heat exchanger that transfers the heat to our radiant floor loop. The loop goes to manifolds which distribute the water to individual zones in the floor.
- Use an Altherma Heat Pump as a back-up system when there is not enough heat in the tank. The Altherma is programmed to run at night during off-peak electrical rate hours to heat the tanks when necessary.
- For cooling, our primary strategy involves the passive design elements we incorporated into the building. To aid comfort and lower humidity, we sometimes run a dehumidification coil in our ventilation system. We also have the ability to circulate cool water through our floor distribution system to cool the building if necessary.
- Adopted a "Topping Off" strategy where we keep the indoor temperature in a tight range and the system is always running, just topping off the heating or cooling when needed. This basically eliminates any nighttime setbacks.
Why is it important?
This hybrid system is important to a building's sustainability because it:
- Directly connects the building and its occupants to the earth's natural systems (e.g. sunlight and air)
- Demonstrates an "appropriate" use of technology (only after the natural systems are unable to meet the needs).
- Includes renewable, high-efficiency, low-carbon components (e.g. solar thermal panels, earth tubes).
- Reduces energy operating costs because of ultra low energy usage.
Early Conceptual Design
To see the current system in action see our building control system page.
Solar thermal panels
The solar thermal panels component captures the energy from the sun and uses it to heat water running through the panels. The panels are connected directly to thermal storage tanks, so the sun's energy is stored in the water in the tanks and drawn on by the radiant floor system when needed.
Mass thermal storage
We have 2 thermal storage tanks, one approximately 3,500 gallons, and one approximately 1,500 gallons, in the annex. They are connected to the solar thermal panels through the roof, and circulate through a heat exchanger. Pex tubing then carries the water to manifolds located throughout our floors. The manifolds circulate the water under our floors to heat the building in a radiant-heating style.
A radiant floor system using water in pex tubing is used to heat the Green Garage building. The system is integrated into the floor system in zones sized to meet the heating demands of the particular zone.
The role of earth tubes and earth room
The main role of the earth tubes and earth room is to make the Altherma heat pump operate more efficiently. Both take advantage of the earth's constant moderate temperature to increase the efficiency of the equipment. The earth room is located in our basement, and the earth tubes originate in our back yard, are buried under the ground along the length of the back yard, and then end in the earth room.
Integration and Controls Design
Integrating all the components of the hybrid heating and cooling system required significant design effort. Some of the controls are manual and some are automated. The key integration areas are:
- The integration of the heat pump with the mass storage system. This is temperature controlled with the heat pump coming on only when needed.
- The changing of the thermal storage from winter heat mode to summer cooling mode is done manually.
- The supply-demand mixing valve for the radiant floors controls the temperature of the fluid in the radiant floor tubing (pex).
- Automation of moisture control with all other components.
- If you are interested in learning more details about how this system is programmed, please see our Sequence of Operations Matrix and click on the appropriate tabs at the bottom of the page.