October 20, 2018
My good friend and colleague, Tex McLeod, and I have been hosting a Building Science Training Camp each spring for builders, manufacturers and energy advisors for the past 5 years. The objective of "Spring Training Camp" is to promote conversation about the latest information on advancing housing technology and to break down the barriers to wider adoption of high-performance buildings. At this year's camp, held in Huntsville, ON in April, one particularly important theme was how to determine the appropriate fuel to service the heating and hot water needs of high-performance homes in Canada. To further the conversation we even held a formal debate (well, more funny than formal) where industry leaders argued whether it was better to use a natural gas or an electric based heating strategy. The debate results coincided nicely with research Natural Resources Canada has been doing over the last 5 years or so at the Canadian Centre for Housing Technology in Ottawa.
The conversation needs to start with the fact that even with all the energy efficiency efforts in Canadian buildings over the last three decades, space heating is the single biggest energy end-use in Canada and the second largest contributor to greenhouse gas emissions (GHG). Thus we need to double down on improving the energy efficiency of buildings through more insulation, better windows and tighter construction. As I have reported before, these initiatives are well underway in new housing and the aspirational goal is to have all new buildings built to a "Net-Zero Ready" level by 2032. Certainly, too, we need to constantly improve the efficiency of heating systems. You might be thinking that there isn't much room for improvement when natural gas furnaces and boilers are now commonly over 95% efficient. This is the crux of the debate; how do we evaluate the impact of heat pumps, air source and ground source with performance coefficients of 2.5 to 5.0 against high-efficiency natural gas heating appliances.
I am not suggesting mechanical contractors and individual homeowners need to take on the burden of this detailed analysis. Thankfully, Natural Resources Canada and many of the major utilities - gas and electric - have been cooperating to communicate the balance point or sweet spot between at least the operating cost, energy efficiency and potential greenhouse gas reductions. There are some very clear outcomes from this on-going work.
First, if the sole goal is to reduce greenhouse gas emissions, its impossible to overlook the compelling operational efficiencies of heat pumps over much of a heating season in all regions of Canada, even in provinces where electricity is generated primarily with high GHG fuels such as coal.
So much so that the first rule is, if you are selling air conditioning this summer, upgrade your customer to a heat pump - air source, mini-splits, cold climate air source heat pumps (CCASHP) or ground source heat pumps (GSHP). The incremental cost of the CCASHP or GSHP will be easiest to justify if your current heating source is electric, oil or propane and where there are incentives but sell heat pumps over straight air conditioning everywhere - even in homes that are currently heated by natural gas. There are even gas utility programs in Ontario currently that will provide incentives for this.
The second rule is if the current heating source is anything but natural gas, (electric, oil or propane) the incremental cost of air source heat pumps will have a simple payback of fewer than 10 years, and in most cases less than 5 years. This is even if the client wasn't looking for air conditioning. A very worthwhile proposition.
To me, the most interesting rule or finding is that a hybrid approach for the approximately 7 million houses in Canada that are heated with natural gas can avoid significant amounts of greenhouse gas emissions and be cost effective for homeowners. The hybrid approach of using a heat pump during milder weather and during electrical grid off-peak hours and natural gas in cold weather and peak electrical use times was shown to be very effective by the NRCan study. More specifically, a heating/cooling system that includes a high-efficiency gas furnace and an air source heat pump (instead of a simple air conditioner) combined with even a simplistic switchover mechanism that can be set by the installing contractor will result in significant greenhouse gas reductions and lower total operating costs for the homeowner.
That switchover point will be of interest to readers. In the long term, we can all imagine smart thermostats tied into electrical rate signals, outdoor weather data and the operational efficiency of the heat pump installed that would fine-tune the perfect moments to switch between the natural gas and heat pump operation. These types of controls are being worked on currently in a cooperating effort between industry, government and utilities, so stay tuned on that. In the short term, an easy approximation is to stay in heat pump mode whenever the COP of the heat pump is above 3.0 to 3.5. This performance is typically determined by the outside air temperature and is listed in the manufactures performance data. You would use a thermostat with an outdoor sensor to switch to natural gas when outdoor temperatures are below the point where the heat pumps COP drops below 3.0 to 3.5. To help with making good heat pump control choices, Natural Resources Canada is developing a new Sizing and Selection Guide for Air Source Heat Pumps. It will be out for public review this fall and full publication by next spring - in time for AC season next year.
There are additional benefits to a hybrid system. It gives your homeowner flexibility in fuel choices over the long term. This may be important in areas that have or will have the time of use electrical or gas rates. Moreover, it gives Utilities relief on peak load demand for their distribution grids. This is of most interest, at the moment, to the electrical grid whereby gas heating in the very coldest of weather reduces the need for turning on supplemental generation plants. This flexibility, in itself, can help to flatten demand loads and reduce electrical rates.
Don't miss the opportunity this winter to have a longer conversation with homeowners looking to add or upgrade air conditioning to their home. Knowing how heat pumps can help future-proof their homes to align with coming new controls and energy alternatives will be of interest to many of your clients.
Written by Gord Cooke.
This article was originally published in Mechanical Business, June 2018