How can Tri-energy compete with Geothermal in operating cost?
Heating systems that run on electricity only, including geothermal are about 40% more expensive to operate just because of the higher electricity (D rate) Hydro Québec charges for to this type of heating system. Because tri-energy incorporates a fuel furnace, the low DT rate applies.
Do the math yourself….
When adding-up the lower cost of electricity to run the heat pump and electric heater as well as all other electricity consumption around the house, the total annual cost of fuel and hydro competes with the cost of hydro for a home equipped with geothermal heating.
Air-source and geothermal heat pumps explained
Fig.1 Below shows a typical heat-pump COP (Coefficient of performance) curve for geothermal, ground-source and air-source heat-pumps.
Air-source heat pump operation.
This type of heat pump is generally used dual energy heating.
It extracts heat from outdoor air. Its output efficiency is reduced as the air temperature
drops (fig.1, brown line). When allowed to run uninterrupted with the 3-Flex control, the
heat-pump output efficiency can remain excellent even well below the –12°C Hydro
Québec DT rate low temperature cutoff point. As mechanical stress on components
increases as the outdoor temperature drops, it is generally not recommended to
run an air-air heat pump at outdoor temperatures below –15°C.
Fig.1 Shows an example of geothermal heat pump output efficiency with
EWT (entering water temp.) of +7°C, when in heating mode.
Practically speaking the efficiency of a geothermal heat-pump can vary between
250 and 400% depending on the actual ground temperature.
Geo-thermal versus Tri-energy .
Thermal energy is absorbed by a liquid circulating below ground through a long, usually closed loop tube. Generally the deeper it runs below the surface, the higher the EWT (entering water temperature) going into the geothermal heat-pump. When the of the ground surface layer starts to freeze over as the winter heating season progresses, the EWT for a shallow loop installation can drop below –5°C, thereby reducing the geothermal efficiency.
The heat-pump “liquid to liquid” heat exchanger extracts thermal energy from an anti-freeze liquid running through the underground loop. And like an air to air heat-pump, refrigerant vapor is compressed and circulated through the indoor heat-exchanger evaporator coil located in the ventilation duct. As air flows through the indoor coil, heat is extracted, raising the duct temperature to about 35°C, changing the coil hot vapor to liquid form.
Geothermal heating consists of a heat-pump with electric element heater hybrid system.
Most geothermal installations in our climate cannot produce adequate heat to keep the house warm during the colder days of winter. To get around this problem, a standard electric element heater is installed in the warm air duct. It delivers “add-on” heat in order to maintain thermostat daytime “setpoint”, as well as for “heat-recovery” following a nighttime thermostat “setback”.
When adding-up all limiting factors discussed, the overall
heating efficiency of geothermal can be disappointing.
Converting to geothermal heating
When converting an existing forced-air heating system to geo-thermal, low airflow of existing ductwork may limit the geo heat-pump capacity. Therefore larger electric heaters are needed to make up the difference.
The high cost and intrusive nature associated with installation a
geothermal system deters many homeowners from embracing this technology.
Geo-thermal versus Tri-energy
When taking into account the higher Hydro Québec D rate for geothermal heating, and
include all other electricity use around the house at this higher rate, the cost of heating with a geothermal system is often comparable to tri-energy that uses a standard gas or oil furnace which makes it eligible for the lower DT rate.
3-FLEX, tri-energy is an excellent alternative to Geothermal
at only a fraction of its equipment and installation cost.
Back-up heat in case of equipment or power failure.
Because a geothermal heating system is all electric, it requires a large standby generator to run the heat pump and HVAC fan in case of heat-pump or Hydro power failure.
With 3-FLEX tri-energy, the fossil fuel furnace can heat the entire house incase of a Hydro outage, requiring only a small standby generator for running the furnace.