MIX AND MATCH … CONTRACTOR EXPLAINS BENEFITS OF A HYBRID SYSTEM

Canadahas long held a leadership role in the development of heating technologies. The early adopters of high efficiency furnaces and combination heating systems were well represented by Canadian HVAC contractors. Now it is time for contractors to embrace new heating options for our long, cold winter weather that can simultaneously provide reliable, comfortable heat while significantly reducing the carbon dioxide emissions from their operation. In new construction, as net-zero energy ready homes move closer to being a reality, building codes offer many options for getting there. Within those options there are seven to eight mechanical opportunities to help builders meet the 2020 National Building Code requirements. These same options will be critical in existing homes as well. Perhaps the most compelling of those opportunities is finding ways to include heat pump-based technologies for space heating. I (GC) recently spoke with Jeff Daley (JD) of Bryan’s HVAC & Fuel Sales about system options and the efficiencies that can be achieved with a hybrid heat pump approach.

JD Many of our customers think of Bryan’s HVAC & Fuel Sales as an oil and propane delivery business, but we see ourselves as a rural heating company. The majority of heating systems we install reduce or eliminate the amount of fossil fuel burned compared to customers’ original heating systems. We are in a unique position in that we have years’ of data on customers’ oil or propane consumption. As shown in Figure 1, we are able to see the impact of improved heating systems on their fossil fuel volume.

GC What was the typical or traditional solution to heating and cooling used up until now?

JD Up until about five years ago propane was

the status quo for rural builds with a handful of geothermal systems.

GC What has prompted the transition to heat pump solutions?

JD We did notice a difference in awareness of heat pumps after the GreenON program about five years ago. The increase in oil and propane prices have also motivated homeowners to look beyond the status quo.

GC Tell us about the heat pump solution(s) you employ and why you like that approach?

JD About three years ago we installed our first “carbon buster” system. That name was a placeholder until we came up with something better, but it has stuck. We use an all-electric style fan coil but instead of electric elements for auxiliary heat we use a hydronic coil heated by a tankless water heater or boiler. This allows the air source heat pump to contribute heat well below the balance point and use the fossil fuel backup to supplement the output of the heat pump. In this case we have found the heat pump provides about two thirds of the annual heating energy and the fossil fuel backup provides about one third of the annual heating energy.

Gord is a professional engineer who has spent 35 years helping builders and HVAC contractors implement innovative technologies into high-performance homes. He has particular expertise in IAQ and airflow management in houses, and can be contacted at gordc@buildingknowledge.ca.

The traditional dual fuel approach of a heat pump connected to a fossil fuel furnace results in the heat pump turning off at the balance point and the furnace doing all the heating work below that temperature. With the furnace and heat pump approach the heat pump generally provides about one third of the annual heating energy and the furnace provides the remaining two thirds.

GC How do you assess or determine which approach to use?

JD With new builds the biggest variable is the mindset of the builder and whether they are willing to try something new. Now that we have installed many of these systems and have a few years of data, more builders are open to the carbon buster approach.

GC What has been the response from builders and homeowners?

JD There has been very little response from builders and we see this as a good thing. We want this system to work like the status quo system would so there is not a steep learning curve for the builder or end consumer.

GC What technical challenges have you faced and how have you overcome them?

JD A fan coil with a hydronic backup is more sensitive to the fine details both from the standpoint of system design and installation. It takes more time when designing a system to make sure all the components are going to work together to provide the desired result compared to specifying a furnace. We have had a few instances where our installation supervisor has had to double check the thermostat configuration as some thermostat settings are configured for an all-electric system and this was unnatural to the technicians initially.

GC In a retrofit situation, does the approach change at all from the new home solutions?

JD With a retrofit type installation we are always talking to the end user so we are explaining the benefits to the person who will benefit. From a technical perspective this is an excellent solution for a home with 100-amp service, which could otherwise not install an all-electric heat pump or geothermal system. It is important to take into consideration the mechanical room ceiling height in an existing home as the fan coil with a hydronic coil on top of it may be too tall to fit into the space.

GC What assessments/tests etc. are you doing to determine the feasibility of these approaches in existing homes?

JD We do a detailed heat loss calculation and carefully consider equipment specifications, particularly the hydronic coil and its ability to provide enough heat at a reasonable water temperature and airflow compatible with legacy duct systems. The flow capability of the circulator built into the tankless water heater has limitations whereas with a boiler we can specify a circulator to better match the needs of a high heat loss home.

GC What are the most significant barriers to a heat pump solution in existing homes? Do you have suggestions as to how to overcome them?

JD Older homes that have a high heat loss and low-capacity duct system are a challenge. In some cases, it is practical to upgrade the ductwork. Discussing the impact of building envelope improvements on the heating system requirements can be helpful. If the homeowner is planning to upgrade the windows or insulate an un-finished basement, these improvements may allow us to specify equipment that will work well after the envelope upgrades are complete.

GC Tell us about any feedback you have gotten from homeowners to the heat pump approach?

JD Customers who have lived in the same house for a few years before the heating system upgrade love the cost savings. In some cases, the heat pump provides air conditioning where there was no air conditioning previously. Interestingly, many homeowners are moving to rural areas for the first time and will upgrade the heating system before spending their first winter in the home. In this case they may not fully appreciate the cost savings; it is more of a cost avoidance strategy.

It is so encouraging that a rather historic and traditional fuel oil and HVAC contractor is an early adopter to embrace one of the technologies. This is going to be so key to the dramatic reductions in carbon dioxide emissions in the millions of older homes across Canada in the next seven to 10 years. As Jeff noted, a hybrid system utilizing a hot water coil after the heat pump allows extended use of the heat pump through the winter. It also allows more flexibility in homes with limited electrical service, smaller duct work and higher heat losses. I really appreciate how Jeff and Bryan’s Fuels are so committed to getting the technical details correct – proper sizing, proper piping and set-up, and thorough commissioning of controls. All professional contractors will recognize the need for even more rigour in the early days of this burgeoning heat pump market opportunity so that there are no bad jobs.