The logical place to look next for utility efficiency after the lighting retrofit has been completed is heating – heating air and water heating. This is why the Heat Pump has been touted as the next “big thing” in energy consumption. In addition to significantly improving efficiency, the Heat Pump is also an essential element of electrification. Understanding what it is, what it isn’t, and how it came to be can help make more informed decisions.
The heat pump has many uses, including providing heating of both air and water. What makes it unique in all applications is how this is accomplished. Conventional heating equipment either uses a flame to burn fuel, in the form of natural gas, heating oil, wood, and coal or if traditional electrical heating, the use of a high resistance material that an electrical current passes thru, the air then passes over this material to create heat.
The issue with both conventional approaches is the lack of efficiency; in some cases, 50% of the energy used is not applied to generating heat. A heat pump can reduce heating costs by up to 60% compared to a brand new furnace. It can accomplish these efficiency levels because instead of creating heat, a heat pump transfers heat from one place to another.
The first underlying theory about how a heat pump would work was described by Lord Kelvin in 1852 and was first developed and built by Peter von Rigginger in 1856. The first use originated while conducting experiments on water vapor’s latent heat for the evaporation of salt brine. The heat pump remained a tool to dry salt until 1945, when a Norwich city engineer named John Summer applied the theory to a building’s heat emitter system by circulating water.
Later, in 1948, in the United States, Robert Webb was experimenting with his deep freeze when he accidentally refined the heat pump concept. Looking to improve his freezer, Robert burnt his hand on the coils of his home freezer. This puzzled him because he thought the coils of the freezer would be producing cold, not heat. This wasn’t just any heat; this was boiling water temperature, scalding hot. Robert began experimenting on what to do with this heat, not wanting to waste it. Eventually, he sent the hot water from the freezer to his water tank to heat the water in the storage tank. That solution only had one problem, he had too much hot water. Cleverly he sent the extra hot water to a fan and blew the air over the copper tubing; the heat was enough to heat his home.
While working models were developed, adoption was not widespread due to the low cost of fossil fuels, resulting in most buildings remained built with separate furnaces and air conditioners. The OPEC oil crises of the mid-1970’s changed that, rising fossil fuel prices and heat pumps began to be experimented with on a grander scale.
By 2008, the United States had installed between 50,000 and 60,000 units per year, and over 750,000 units were in operation worldwide. As the climate crisis began to grab headlines, efficiency became the most cost-effective strategy to reduce impact. By this time, heat pumps had evolved into water source, air source, and geothermal source, increasing efficiency.
So how does this apply to my portfolio, how can I use this to help reduce my impact?
There are two areas in which heat pumps potentially have a role in reducing the energy consumption of your property:
- Hot Water Heating
- Heating & Cooling
According to US Energy Information Administration statistics, water heating accounts for 24-32% of US end-use energy consumption by housing type for apartments. The more units a property has, the closer to one-third that number gets. Yet, how often do you hear a conversation about the energy consumption of the domestic water heating system? In some ways, this energy thief has wholly avoided the discussion. We are much more likely to talk about lighting, representing only 6% of home energy consumption. In the right circumstances, lighting makes a lot of sense, but it’s not always the automatic no-brainer it used to be.
The most common water heater remains the storage hot water tank. Whether using electrical resistance or natural gas, this hot water heating method entered the built environment in the late 1800s, when Edwin Rudd designed the first safe “automatic, storage-tank gas water heater.” At the time, this marked a vast improvement over the more common method of heating a pot of water over a fire and pouring it into your bath. However, except for adding insulation and the technology of electrical resistance instead of gas as an option for the heating source, not a lot has changed over the next 100 years.
Today most standard gas water heaters have an efficiency factor of .58-.60, meaning that only about 58-60% of the energy used to heat the water is converted into heat. Energy Star models currently have a minimum efficiency factor of .67, although some manufacturers make models in the .67-.70 range. While an improvement, that is still a lot of wasted energy. Compared to gas hot water heating, electric tanks are much more efficient, with an efficiency rating of .90, while high-efficiency models can reach .94-.95. Due to the current gas costs, while less efficient, the gas may cost less to operate currently, but a gas water heater must vent the spent gas taking with it some of the heat, which results in a more significant loss of efficiency compared to electric.
The efficiency rating for a heat pump water heater far exceeds either the gas or energy star electric tank heater, with some models reaching an efficiency factor of 2.0. You read that right, 200%. At first, that may sound strange, but remembering the efficiency factor compares the amount of hot water produced per unit of electricity consumed in a typical day, so in English, the heat pump water heater produces twice the amount of hot water as the amount of energy used. This means reducing the energy consumption of nearly half the consumption an energy star electrical resistance tank would have used and reducing almost 75% of the energy if using gas. Significant by any account.
What makes this strategy more enticing is a growing number of utility incentive programs that recognize the opportunity presented by heat pump water heaters which can further reduce the initial investment.
The lifespan of that tank water heater is somewhere between 10-15 years (the harder your water, the shorter the life), and once installed, it is a device that we tend to give very little thought to until we step into a cold shower. Even if your property has water heaters that are not yet at the end of life, working with a consultant now to evaluate the opportunity may prove to be a smart strategy to both reduce operational expense and environmental impact.
The second application is heating; while more common in Climate Zones 1-5, many properties condition the space with either gas or electrical resistance heating instead. I should note that we also see hydronic loops in this space, especially in older, mid-to high-rise apartments.
Heat pumps are often misunderstood, as they operate on a different principle than gas, electrical resistance, or boiler-type heating. As explained at the beginning of this article, instead of applying heat to the air to condition it, the heat pump transfers heat between the heat source (ground or air) and the conditioned space. The result is when you walk by a vent with a heat pump; the air may not feel as warm as direct heat is not being applied. This can cause confusion, but the reasoning is really because of us.
Heat pumps generally produce air that is between 85-92 degrees, so with our body temperatures at 98.6 or thereabouts, the air coming from the vent seems cooler. However, it is unlikely that many truly keep their homes above 92 degrees. To overcome the cold air inside the space, with gas, electric resistance, or hydronic loop, the air temperature coming out of the vent is more likely in the range of 130-140 degrees. Back to our body temperature at 98.6, of course, the air feels warmer with these other systems. The trick is, it has to produce that additional heat to overcome the inefficiency of the design.
Heat Pumps have come a long way since their initial discovery, and recent technology has forced engineers to rethink their application. Just a decade ago, as soon as we reached climate zone 6, engineers would change technologies away from heat pump installation. Today we are seeing heat pumps performing well in frigid climates; in fact, Maine (Climate Zone 7) has set a target of 48% of all homes to utilize heat pumps by 2030. Similarly, Massachusetts has set a goal of 40% by 2030, and Colorado has a goal of 60% by 2030.
The bottom line on heat pumps is whether used to heat water or heat air; they have a proven track record of superior efficiency compared to gas and more conventional electrical resistance heating. It is also really not a new concept, it just seems new, but the science has been proven over time. As these devices typically have a shorter life cycle than the buildings they are installed in, it makes a lot of sense to consider this technology if it is time for capital improvements. What might not seem as obvious is the efficiency is so much better. Especially when paired with utility incentive programs, it may make sense to proactively replace them ahead of your regular capital improvement schedule, particularly as we move towards electrification of the built environment.