Chapter 1
Introduction: The Renewable Heating and Cooling Project
This Renewable Heating and Cooling (RHC) study focuses on the electrification of space and water heating in Boulder’s residential building stock. DNV GL, in collaboration with Radiant Labs, Meister Consulting Group, and intern Graduate Students from University of Colorado Boulder have determined heat pump technology to be the most scalable, cost effective, flexible, efficient electric technology to shift fuel consumption for thermal energy use in buildings from natural gas to clean electricity.
This study focuses primarily on air-source heat pumps (HPSH) for space heating and cooling, including ductless and ducted systems, and, heat pump water heaters (HPWH).
The project was done alongside 3 other cities simultaneously working through the same process as part of an Urban Sustainability Director’s Network Innovation fund project. The 2017 RHC Project is one part in a multi-year, multi-city project with New York City, Burlington VT, Washington DC where these lead cities and 20 observer cities have set thermal decarbonization as a priority. Decarbonizing thermal energy use in buildings depends on, first increasing quantities of renewable electricity and prioritizing the use of clean electricity over fossil fuels, then electrifying thermal systems for space heating/cooling and water heating using highly efficient technology.
This study focuses primarily on air-source heat pumps (HPSH) for space heating and cooling, including ductless and ducted systems, and, heat pump water heaters (HPWH).
The project was done alongside 3 other cities simultaneously working through the same process as part of an Urban Sustainability Director’s Network Innovation fund project. The 2017 RHC Project is one part in a multi-year, multi-city project with New York City, Burlington VT, Washington DC where these lead cities and 20 observer cities have set thermal decarbonization as a priority. Decarbonizing thermal energy use in buildings depends on, first increasing quantities of renewable electricity and prioritizing the use of clean electricity over fossil fuels, then electrifying thermal systems for space heating/cooling and water heating using highly efficient technology.
A growing trend in leading cities around the world is the push towards electrification both in the transportation and in heating and cooling technologies. This study followed the steps in chart below to develop key strategies to dramatically increase electrification and decarbonization of thermal energy:
The significance of natural gas emissions
Natural gas usage represents nearly a fifth the City of Boulder’s emissions. While efforts to decarbonize the electricity sector have taken significant steps forward over the past decade, there has been very little progress in reducing dependence on natural gas usage in either the residential or commercial/industrial sectors.
In 2016, as part of approval of its new climate action plan, the city of Boulder committed to achieving 100% renewable electricity by 2030.
As progress is made towards that goal, the share of emissions being generated by natural gas will increase significantly and may represent as much as 50% of the city’s emissions by 2030.
In addition to its increasing share of Boulder’s remaining fossil fuel dependence, the climate impacts of natural gas may also have been significantly underestimated. Methane, the key constituent of “natural” gas is a highly damaging agent in the upper atmosphere with estimates ranging between 30-70 times the impact of CO2. As new information emerges regarding the increased leakage rates for natural gas at both the generation and distribution levels, the overall impact of natural gas on the climate—and local environments—is being revised, showing significantly higher impacts than previously thought. For every 1% increase in leakage rates, the estimated impacts of natural gas on the climate increase by 10%. While natural gas was promoted as a clean fuel decades ago, science now shows that renewable electricity is the “clean fuel” that cities need to switch to in order to achieve their long-term greenhouse gas reduction goals of 80% by 2050 or sooner.
As part of its approved 2016 climate action goals, the city has set specific targets around the reduction in natural gas usage. These efforts are described as part of larger efforts to replace fossil fuels with renewable energy alternatives. The section of Boulder’s climate action plan outlining these actions and the specific targets set for achieving this objective are displayed in the figure below
In 2016, as part of approval of its new climate action plan, the city of Boulder committed to achieving 100% renewable electricity by 2030.
As progress is made towards that goal, the share of emissions being generated by natural gas will increase significantly and may represent as much as 50% of the city’s emissions by 2030.
In addition to its increasing share of Boulder’s remaining fossil fuel dependence, the climate impacts of natural gas may also have been significantly underestimated. Methane, the key constituent of “natural” gas is a highly damaging agent in the upper atmosphere with estimates ranging between 30-70 times the impact of CO2. As new information emerges regarding the increased leakage rates for natural gas at both the generation and distribution levels, the overall impact of natural gas on the climate—and local environments—is being revised, showing significantly higher impacts than previously thought. For every 1% increase in leakage rates, the estimated impacts of natural gas on the climate increase by 10%. While natural gas was promoted as a clean fuel decades ago, science now shows that renewable electricity is the “clean fuel” that cities need to switch to in order to achieve their long-term greenhouse gas reduction goals of 80% by 2050 or sooner.
As part of its approved 2016 climate action goals, the city has set specific targets around the reduction in natural gas usage. These efforts are described as part of larger efforts to replace fossil fuels with renewable energy alternatives. The section of Boulder’s climate action plan outlining these actions and the specific targets set for achieving this objective are displayed in the figure below
electrification of Residential Heating & Cooling
The significance of decarbonizing residential heating and cooling and the potential impact of increased fugitive emissions is illustrated in Figure 1. This graphic assumes that the electricity used for either charging electric vehicles or running a household air source heating/cooling (ASHC) system come from 100% renewable sources. As the graphic illustrates, decarbonizing household heating can eliminate even more climate damaging GHGs than driving an electric vehicle if a full accounting of natural gas’ fugitive emissions is included. For an average household in Boulder, replacing their existing natural gas furnace with renewable electricity driven air source heating could reduce emissions by over 5 tons annually. If all 40,000 of Boulder’s single family housing units were similarly decarbonized, this would represent a savings of approximately 200,000 mtCO2e.
Overall, switching to clean electricity sources and uses will enable Boulder to meet stated Climate Goals while also improving ambient air quality in the region and inside homes/buildings
Transition to 100% renewable electricity and electrification
Achieving deep decarbonization of residential heating and cooling is contingent on parallel efforts to source 100% renewable electricity for electric-based heating and cooling systems being installed. Boulder has been actively engaged in efforts to achieve this goal through pursuit of municipalisation of its local electric distribution and generation procurement system. That effort is still underway. Whether it is through creating a municipally owned and managed electric utility or through state utility policy reform, Boulder is committed to achieving 100% renewable electricity by 2030. Boulder climate and energy goals are:.
The pathways to achieving this objective will likely include a combination of both local generation and regionally procured utility scale renewable generation. While full decarbonisation of all residential electricity used will require this larger effort, Boulder’s residential RH&C strategy is being designed to enable significant emissions reductions by pairing electric heating and cooling system adoption with solar deployment—either household scale or community solar subscription. This is being coordinated through a larger initiative referred to as the “Roadmap to Renewable Living” that provides homeowners with a simple four-step process to transition all of their household energy needs—including transportation—to renewable energy based systems. More information on this bundled approach to household energy system transition can be found here: bouldercolorado.gov/climate
The Benefits of Electrifying Natural Gas Heating & Cooling Systems
The basis of Boulder’s renewable residential heating and cooling initiative is the replacement of natural gas furnaces, boilers and water heaters with a new generation of high efficiency electricity-based air source heating/cooling appliances. This technology utilizes the same “heat pump” technology that has successfully driven both household and commercial refrigeration for nearly 100 years. These technologies are now the dominant form of heating and cooling in most of the rest of the world. Due to the prevalence of natural gas in the US and other parts of North America, air source/heat pump systems have been slower to penetrate heating and cooling markets in this country. Heat pump space and water heaters offer many benefits, beyond carbon reduction, including improved comfort and safety, the ability to provide both heating and cooling, greater flexibility and controllability, and the potential use in larger management of local and regional grid energy demand.
The Top Benefits Include
The Top Benefits Include
Improved Household Comfort
Efficiency
Electrification and energy resilience
Environmental
Economic
|
Cooling with e-heating in one technology
Improved Health and Safety
|
Chapter 2
Forecasting Boulder's Residential Heating and Cooling
characterizing boulder's building stock
Boulder is a city of 107,000. It has grown from a population of close to 86,000 in 1990. It is projected to reach 122,750 by 2025 based on its projected land use build out capacities.
The primary residence of the existing population is single-family detached homes, half of which are owner occupied properties. Boulder’s homeownership rate is well below that of other surrounding communities and the county due to the presence of the University of Colorado, Boulder, and its 32,775 students (2015).
Additions and remodels provide an opportunity for the City of Boulder’s development services department to influence the type of heating system which is installed or replaced. The table below outlines the number of permits seen in each year for additions or remodels. At approximately 1,000 permits projects per year, a full quarter of Boulder homes seek and addition or remodel per decade.
Characterizing Boulder's Existing Residential Heating & Cooling Systems
At almost 35,000 units, central furnaces are the vast majority of systems in Boulder. At around two percent, the saturation of heat pumps in the Boulder market is small, and likely surpassed by nearly every other space heating technology available. The chart below shows the estimated number of residential heating systems in Boulder broken down by system type. Each system type will affect a different path to electrification.
Based on Radiant Labs research, 202 households have installed a permitted heat pump space heating systems since 2000. However, the number of HVAC permits pulled is much lower than would be expected given the useful life of the HVAC systems. A report by the governor’s budget office estimates heat pump space heating saturation at two percent in the state of Colorado. At this ratio, 870 homes in Boulder would utilize heat pumps for space heating. Stakeholders from the Boulder working group determined 600 heat pumps to be a fair estimate of existing stock within City of Boulder homes.
As we discussed, we need to set an estimate install number which I think would likely be around 600 and then provide some rationale for how that number was derived.
As we discussed, we need to set an estimate install number which I think would likely be around 600 and then provide some rationale for how that number was derived.
Customer profiles or archetypes have been developed for the top priority potential customers in Boulder based on building characteristics, demographic and social indicator analysis.
customer segmentation
In Boulder, there are several Early Adopter Archetypes, representing the profiles of consumers who would be likely to adopt heat pump technology. Many of these consumers either lack air conditioning or are likely to need a replacement in the next five years. Consumers who have previously participated in energy efficiency programs may be more open to adopting a new technology, particularly when there are incentives. Aside from those who care about the environment, early adopters may often be motived by cost or comfort concerns, either reducing heating costs in areas where natural gas is unavailable or replacing outdated and inefficient equipment. A survey of existing heat pump customers demonstrated a range of motivations for selecting heat pumps with the primary reasons as follows: efficiency, comfort, adding cooling, and utilizing with solar. The existing customers are not representative of the broader market of average homeowners in Boulder; however, they provide insight into the mindset of early adopters.
Chapter 3
technology summary for heat pump space and water heating
Heat pumps use the refrigeration cycle, run in reverse, to efficiently make heat without the requirement for on-site combustion of fossil fuel. When selecting central or ductless air conditioners for homes and buildings, this means that a heat pump option can be included for the additional cost of a reversing valve, typically a 3-5% cost increase of $200-400.
A heat pump requires a heat sink from which to pull heat which is pumped into the space. In common residential applications, there are two basic options:
A heat pump requires a heat sink from which to pull heat which is pumped into the space. In common residential applications, there are two basic options:
Ground Source Heat Pumps
Commonly called “geothermal,” ground source heat pumps utilize the consistent temperature of the earth to provide a source for heating and cooling of a home. This consistent temperature allows them to operate extremely efficiently, up to 8x as efficient as a gas-fired furnace. In certain applications, particularly those who desire extreme efficiency, there is no better choice.
However, the installation is expensive. Holes are bored into the ground, up to 300 feet deep, and piping is inserted into the holes which pumps a water-glycol solution to-and-from the heat pump unit. The large land requirements an expensive cost of boring make ground-source heat pumps unrealistic at scale for Boulder. Moreover, when geothermal loops reach end of useful life, the thousands of feet of plastic are abandoned in place, an environmental concern. |
Air-Source Heat Pumps
Air-Source Heat Pumps (ASHP) use the heat embodied in the outdoor air, which always contains heat as long as we’re in earth’s atmosphere, as a source to heat the space or water. In cooling mode, heat is rejected from the building to the outdoors. Air-source heat pumps are 3-4x as efficient as gas-fired equipment, are reasonably priced, and easy-to-install. The rest of this report will focus on air-source heat pump technology, which comes in two basic configurations:
Unitary Systems
The entire system is housed in a single unit. The most common application for heat pump hot water heaters, this is less common in residential space heating and cooling. |
Split Systems
The “condensing unit” is installed outdoors to provide access to outdoor air, and houses the compressor and other equipment. Inside, a coil transfers heat to water heater or space conditioning system. If you have central air, it’s probably a split system |
heaT PUMP SPACE HEATING
Heat pump space heating retrofits provide the biggest opportunity for carbon emissions reductions within Boulder homes. This will be even more apparent when Boulder’s electricity becomes 100% renewable by 2030. With electric vehicles starting to hit stride, space heating may well the biggest carbon emitter within Boulder City limits.
There is more than one way to skin a climate-destroying heating system. Electric furnaces, radiant heating systems, solar-hydronic, biomass combustion, and electric hydronic systems can all meet the goal of renewable heating. However, air-source heat pumps provide the most efficiency and cost-effectiveness within a package that is easy to install with technology which has been around for decades and is available today.
The first heat pump was invented in by Peter von Rittinger in 1857, and heat pump space heating systems have been widely used in the United States since the 1980s. Increases in efficiency and low-temperature heating performance which have occurred over the last decade have made the technology ripe for wide-scale implementation to reduce carbon emissions in both mild and cold climates.
There is more than one way to skin a climate-destroying heating system. Electric furnaces, radiant heating systems, solar-hydronic, biomass combustion, and electric hydronic systems can all meet the goal of renewable heating. However, air-source heat pumps provide the most efficiency and cost-effectiveness within a package that is easy to install with technology which has been around for decades and is available today.
The first heat pump was invented in by Peter von Rittinger in 1857, and heat pump space heating systems have been widely used in the United States since the 1980s. Increases in efficiency and low-temperature heating performance which have occurred over the last decade have made the technology ripe for wide-scale implementation to reduce carbon emissions in both mild and cold climates.
Replacement versus displacement
Once 2030 hits, Boulder will need to start pulling gas meters to meet their climate goals. However, in the interim, while technology is developing, not every therm of gas use has to be removed at once. In difficult installations, it might make sense to displace a large chunk of gas usage with HPSH, as opposed to a full-scale fuel switch.
Examples when displacement might be preferable:
Examples when displacement might be preferable:
- Single Zone Ductless in Heavily Used Zone: If the primary need for comfort heating is a bedroom, or air conditioning is being added to a living room, a low-cost solution would be to install a single-zone ductless mini-split in that particular zone. This will enable high-efficiency electric heating or cooling in that zone at a low cost. Gas would still be burned to keep the home warm when guests are around or to ensure pipes don’t freeze. But 50-80% of gas used for space heating can be offset.
- Central Ducted System in Large Home with Gas Backup: A standard residential gas furnace is sized at 80,000 BTU, but the largest central ducted HPSH is 60,000 BTU. In addition, HPSH capacity decreases slightly with ambient temperature depending on manufacturer. In a large home, on the coldest of nights, full electric replacement could mean requiring two central systems (doubling price) or an 80 Amp upgrade to the electric system ($2-4k.) The displacement scenario would maintain a single system by installing a heat pump A-coil attached to the existing furnace, and keep the gas connected to handle peak heating hours. Gas will likely be used for less than 10% of heating hours in this scenario.
configurations: ducted or ductless?
Ducted Heat Pump Space Heating
Ducted systems look identical to existing central air conditioning or central furnace systems. Refrigerant piping runs from the outdoor condensing unit to an “air handling unit” located indoors. From there, hot or cold air is blown throughout the home via ductwork which delivers air to each room via vents (aka grills, diffusers, registers, etc.) Ducted systems are the simplest one-for-one replacement of existing central furnaces and air conditioners. Pros:
|
Ductless Heat Pump Space Heating
Ductless systems, often called “ductless mini-splits” are common in Asia-Pacific buildings, commercial buildings, and low-rise hotels. Since 2005, these systems have been gaining acceptance in the US market. Refrigerant piping runs from an outdoor condensing unit directly to units located in each room of the house. Pros:
|