By Jeff Weston, P. Eng. IMEC Mechanical
Thermenex at LangaraBuildings Environmental Building Mechanical & Electrical (HVAC) Systems Environment
At Langara College in south Vancouver, Building-C was recently renovated and connected to the new Langara Student's Union building. The combined multiuse complex designed by Teeple Architects is 5,463...
At Langara College in south Vancouver, Building-C was recently renovated and connected to the new Langara Student’s Union building. The combined multiuse complex designed by Teeple Architects is 5,463 square metres and five storeys, incorporating offices, classrooms, studios, restaurants and a bookstore.
The goal was for the building to have minimal greenhouse gas emissions and maximum energy savings. The obvious answer was to use a ground source (geoexchange) system; a 90-ton vertical ground loop system was installed. Less obvious is that the ground source system is the least efficient heating system in the building.
The project is the first application of a patent-pending technology called Thermenex. Thermenex uses a water-filled pipe that functions as a hub for thermal energy exchange. The pipe is not a loop; it has no pumps; it is simply a long length of pipe (with a temperature differential from one end to the other. A “thermal gradient header” (TGH) is the best description. The water can flow in either direction depending on the secondary pumping systems and controls.
Essentially, the building heats and cools itself. The use of a thermal gradient header pipe for all the building’s heating and cooling systems allows all heating loads to be considered as cooling sources and all cooling loads as heat sources.
The system targets zero thermal energy waste, with heating and cooling added for peak demand. No need for solar panels — the building is a solar heat collector. No ‘free’ cooling — the building needs heat when it is cold outside. When the building is unable to heat itself, the ground source system is used.
At Langara College, the thermal gradient header pipe is 100 mm diameter and about 250 metres long. It serves the entire Langara-C and Student Union complex, as well as some neighbouring buildings.
The first stage of heat is extracted from any cooling load, such as computer rooms, electrical rooms, and interior spaces.
When the sun is shining on a cool day, free cooling is not used. Instead, the heat from cooling the sunny side of the building is transferred to the header and used to heat the building’s other side.
When the building requires more heat, the second stage of heat comes from cooling the exhaust air. Standard water source heat pumps are used to heat the water in the header by cooling the exhaust. The system has COPs (coefficient of performance) ranging from 5.2-6.8. This is twice as efficient as ground source heating.
What the geoexchange system is best for is cooling. Why? Because the ground is cold and that makes it an efficient place to reject heat. The ground source heat pump is more efficient than a typical chilled water system. What is another source of cooling? Stated another way, what else needs heat? Since the water can flow in either direction in the header for thermal exchange, a DHW Heat pump is connected to the header and it provides cooling for the building.
Every heating and cooling system takes water from the header at the temperature it needs, increases or decreases the water temperature, and returns it to the correct portion of the header using control valves. Thus the mechanical design uses systems that function with the coolest “hot water” and the warmest “chilled water.” The efficiencies and energy exchange potential is maximized by using minimal water flow and maximum temperature change, which in turn minimizes energy transportation costs.
The building has been submitted for LEED Gold certification, with all 10 energy points. About 75% of the annual heating energy comes from thermal exchange within the building. The independent energy model predicts energy savings of 65%. Not bad for a building with no natural ventilation and no “free” cooling. (If you think about it “free cooling” is “heat wasting.”) The building systems include radiant heating and cooling in the slab, chilled beams, induction units, heat pumps and air-handling units with a single heating/ cooling/reclaim coil.
The system is still being commissioned but the early numbers are very promising. The per square foot electrical energy consumption — which includes heating — is less than half that of the existing buildings which are heated by a gas fired central boiler plant. And these numbers were taken when the system was not fully optimized. Best of all: no greenhouse gas emissions.
A thermal gradient header can also be used for district energy sharing. Langara College is looking at the possibility of using the Thermenex system to “harvest” thermal energy from the central cooling plant and using exhaust air from the existing building stock to heat new facilities that can take advantage of low grade heating systems.
Mechanical/design build & Thermenex inventor: IMEC Mechanical (Jeff Weston, P. Eng.).
Architect: Teeple Architects.
Electrical engineer: Genivar.
General contractor: Bird Construction