As more and more heat pumps are installed in new homes and retrofits, we’ve had an increase in questions from homeowners and tenants about how to correctly operate the equipment. The installations come with Seven-day Programmable Thermostats, required under the Title 24 energy code, however, there is a need to help occupants correctly use those thermostats to optimize heat pump efficiencies and improve thermal comfort.
“Right-sizing” Temperature Setbacks
For decades, California has worked to improve the efficiency of furnaces and air conditioners in homes and offices by engaging the public to adjust thermostats at certain hours. Programmable thermostats are now a code requirement and the State provides instructions on how to schedule thermostats to meet efficient temperature use during occupied and unoccupied hours. While this approach was helpful in the past, the schedule for using heat pump fan coils, a newer and more efficient heating technology, is different. The recommendation is to leave the heat pump operating at all hours of the day. Setting back your thermostat and scheduling setbacks when the home is unoccupied is still a good idea, but instead of turning the system off, or setting it back 8-10 degrees, set it back 3-5 degrees.
A typical furnace for a single-family home provides between 140-170 degree (F) air from the burner, which reaches about 120 degrees when it enters the room. For homes with heat pumps, air typically enters the room at about 85-92 degrees. Although both temperatures are sufficiently hot enough to heat a home and keep us comfortable, we experience the room environments differently. We’re familiar with the on/off cycle of a furnace, which delivers a large amount of heat that lasts 10-20 minutes before the furnace refires and deposits hot air into the space again. Heat pumps, on the other hand, need to be operated more consistently to maintain comfortable temperatures, since the air they produce is less hot compared to the furnace system.
Thermodynamics
To better understand why heat pumps need to operate consistently and how they can create more comfortable conditions compared to furnaces, it’s important to address how the human body perceives comfort.
The human body perceives comfort based on two factors: heat and moisture. We transfer heat through conduction (our feet on the floor), radiation (heat from our bodies to the space including surfaces), and convection (air moving around the space). Since most of our comfort is determined by the temperature of surfaces surrounding us through radiant heat exchange, keeping our walls, floors, ceilings, and counter areas warm will make the space more consistently comfortable than relying on the air temperature.
Efficiency
One might think this type of heating will result in higher energy consumption and larger utility bills. This is where the integrated “inverter” technology comes into play. This technology, which is now standard in most heat pump fan coils, allows for variable speeds.
The following graph shows the cycling pattern achieved by using inverters. By reducing the temperature drift, the systems operate more efficiently because they do not need to run at full capacity. In fact, the systems operate most efficiently when they are run continuously!
Furnaces typically have an efficiency rating, called the Annualized Fuel Utilization Efficiency (AFUE), of 80%-95% depending on the quality of appliance. This means that only 80% of the energy in the natural gas is being converted to heat at the furnace. Heat pumps utilize a different efficiency metric, the Coefficient of Performance (COP), which is the ratio of useful heat provided versus the work (or energy) required. A COP has a typical range between 3.0 and 4.0, depending on the appliance. A COP of 1.0 is 100% efficient, meaning that heat pumps can be 300%-400% efficient in terms of heat provided and the energy required to produce it.
Helping Californians Adjust to Changing Technology
As the energy code continues to favor energy efficiency and clean electricity, heat pump technology is the go-to solution for mechanical systems. Building officials, design professionals and contractors can support a successful transition by helping owners and occupants understand the efficiency and comfort of consistent temperatures in heat pump operations.
Contractors can enroll in the 3C-REN Single Family program to receive incentives for actual metered kWh and therm savings. Residents can submit an interest form, which lets enrolled contractors know they are interested in installing energy efficient measures. The program is for residents of San Luis Obispo, Santa Barbara, and Ventura Counties.
For more information or to complete the interest form, please visit the 3C-REN Contractor participation page at 3c-ren.org/contractor-participation. Residents can complete an interest form at 3c-ren.org/for-residents
For more information and in-person trainings, please check out our events calendar at 3c-ren.org/calendar-of-events-and-trainings
The on-demand webinar page is at 3c-ren.org/on-demand-trainings
And feel free to reach out to the Code Coach Hotline for more information or to have your questions answered! 3c-ren.org/energy-code-coach
