Heat Pumps- Replace, Repair or Upgrade to Geothermal

The first sign of trouble was when I woke up one morning thinking that it smelled like rain. I was in bed with the air conditioning system on. I could think of several excuses why I might have had that thought and so ignored the first symptom and it would be a several more weeks until the heat pump failed. It was a relatively long and cool spring with nights in the 60’s cooling the house, but come the first 90 degree day  I knew my split system heat pump had failed.

My heating and cooling system like a lot of newer homes in northern Virginia is a split heat pump system that consists of an outdoor metal cabinet that contains the condenser and compressor and an attic unit that contains the evaporator coil and the air handler that sends the cool air through the duct system in summer and hot air in winter. In the heating cycle, the air-source heat pump takes heat from the air outside the home and pumps it inside passed refrigerant-filled coils. Inside the heat pump system are two fans, two refrigerator coils, a reversing valve and a compressor. The outdoor unit contains a coil and fan and the compressor. The reversing valve switches the direction of refrigerant through the cycle and therefore the heat pump may deliver either heating or cooling.

The effectiveness of a heat pump is based on the temperature difference between the source and the sink and which cycle it is in. Heat pumps are more effective for heating than for cooling if the temperature difference is held equal. This is because the energy used to power the compressor can be converted to useful heat when in heating mode and released into the house as extra heat. The condenser is normally outdoors and during the cooling cycle, and the compressor's dissipated work is not put to a useful purpose. Air heat pumps are best suited to relatively warm climates, such as the southeastern U.S. This is because when temperatures are low, a heat pump’s Coefficient of Performance, COP falls dramatically. According to the Department of Energy a7.5-ton rooftop heat pump that has a high-temperature COP of 3.0 can have a low-temperature COP of 2.0 or even lower. And at very low temperatures, a heat pump can require supplemental heat, typically in the form of electric resistance just to function further reducing effective heating efficiencies.

The most effective type of heat pump is the geothermal heat pump. In winter it collects the Earth's natural heat either through a series of pipes, called a loop, installed below the surface of the ground or submersed in a pond, lake or well. The temperature six feet beneath ground surface is cooler in summer and warmer in winter than the ambient temperature and fairly constant, but many loop systems are not installed deep enough in a suitable medium to maintain constant temperature, but nonetheless draws excess heat from the house and allows it to be absorbed by the Earth. I had always assumed that when the time came I would replace my heat pump with a geothermal unit.

Despite the fact that my heat pump system is under 8 years old and heat pumps should last 12-14 years, the evaporator coil corroded and leaked enough Freon (R22) that the system could no longer cool.  The corrosion of the coil was obvious upon inspection, but the Freon level had been fine 2 months earlier when the system had been serviced, so I was taken a little by surprise to find myself having to make the decision about whether to replace the coil, replace the entire system with an energy star heat pump or upgrade to a geothermal heat exchanger now. A heat pump should last longer than 8 years. This is the first major repair the system has required and I probably could get a couple more years out of the system if I replaced the coil, but there is no guarantee and the outdoor unit had started to show rust two years ago. If I replace the entire system, I will probably get another 8-10 years before I have any major problems.  

In truth we were never happy with the system; it could never keep the master bedroom cool in summer. The master bedroom has unobstructed southern exposure and though we installed drapery, window films and additional insulation as recommended by the Building Envelop Research of US Department of Energy Efficiency and Renewable Energy Unit, still the bedroom was never cool enough in summer. The attic, crawl spaces, and eves, were insulated with cellulose. The pipes, end caps, knee wall, sump pumps and all identified areas were sealed, while my energy bills were reduced significantly, I could not get the bedroom cool on the hottest days. In the winter the passive solar helps and I keep the house at 67 degrees Fahrenheit, which the heat pump has never had any problems maintaining. This is an opportunity to make sure that the heating and cooling system are sized and ducted optimally for my house and lot. The Manual J calculation showed my existing heat pump to be slightly undersized for the house.  The Department of Energy has lots to say about ducting problems with air handling systems.  In a typical home, about 20% of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts. The result is higher utility bills and difficulty keeping the house comfortable, no matter how the thermostat is set. The heating and cooling represent 40%-50% of power use in the typical American home.  An analysis of my electric bills showed that the heat pump operated on average about 7 months a year and that I spent about $1,260 annually operating the system. (My electric rates have been steady for over 5 years and my solar panels supply all my other electrical needs.)

 Most manufacturers advertise energy savings of up to 35%-75%; using an average existing system as a starting point and converting to a geothermal system. DOE states that with an energy star system,  it is possible to save 10%-20% of energy cost from an existing system, giving an implied savings of 15%-35% for a geothermal system versus a new energy star system. If I assumed that the geothermal heat pump would save me 50% of the electricity used for operating the heat pump that is about $600 per year.  There are several calculators on manufacturer's web sites to perform better calculations. I found the Bosch calculator and used it  for projecting savings from a geothermal system as compared to an EER 13 air to air heat pump.  The Bosch website calculator gave me a savings of about $971 with $295 of the savings from hot water heating using inputs for a well-insulated home in the Washington DC metropolitan area converting to a geothermal heat exchanger from a propane heated water and air heat pump. So my back of the envelope calculation was not a bad guess and the hot water heating cost is an important element in the cost calculation.

 Until December 31,2016 a 30% federal tax credit is available on the total cost of a qualifiedheat exchanger, reducing the capital cost. The largest hurdle to the widespread adoption of GHP technology is the one I am facing now- the capital cost for initial installation. The heat exchange loop portion of the GHP system can be half or more of the overall geothermal heat pump system cost (and equal to the total cost for a traditional furnace and air conditioner). However, the geothermal heat pump requires st least 75 feet of tubing (in my case either vertical wells or standing column wells) for each ton of size. The costs I have been quoted were $3,000-$4,000 per ton for installation of the heat exchange loop or well.  The difference in cost was the amount of damage that would be done to my garden. If indeed it is a 4 ton system that the house needs, the additional cost of the geothermal heat pump would be a minimum of $12,000 and could be as much as $16,000 plus any costs to reconfigure piping in my completely finished basement. Even with a 30% federal tax credit for the entire system the payback might take 10 or more years if the actual savings turned out to be 50% of the electricity used by the air heat pump system.

It now appears that this decision is a close call and I need to get detailed proposals to determine the actual cost, the damage to the house and garden, the Coefficient of Performance, COP, and Energy Efficiency Ratio, EER to obtain a better estimate of capital versus operating costs. Also, I need time to think about the benefits of an absolute reduction in energy usage while still maintaining my creature comforts. Installing the right size equipment for the home is essential to getting the best performance and comfort, and now is my opportunity to verify that the new system I install is sized correctly for the house and lot. A system that’s too large will not keep your home comfortable because of frequent ‘on/off’ cycling, but a system that is too small will not be able to cool the house on the hottest of days. Also the duct system which has already had all the leaks sealed needs to be evaluated for adequacy and optimal layout. The system selected will have an impact on reliability- at least according to Consumer Reports.  Finally, I need to make sure that the HVAC contractor I hire has insurance, contractor’s license without complaints, and good references for similar sized and types of projects. 

Reducing My Energy Consumption

I have been systematically making small changes to my home to reduce my energy consumption. I started with the easiest steps; lowering the thermostat in the winter and raising the temperature in summer, purchasing energy star eligible appliances and choosing an LCD TV over a plasma (an LED TV is even more energy efficient, but was not available at the time). The next simple step was to change all the incandescent light bulbs for florescent bulbs and when I installed additional lighting it was florescent fixtures. (Though, I warn that the clothes in my closet look oddly colored in florescent light.) The next project was to install solar films on the windows and patio door and drapes and curtains on all the windows. These were small steps, but I learned over the years that small steps do add up.

The following year, after servicing the heat exchanger and furnace to ensure they were working properly, and appropriately sized for the house, and inspecting the attic and accessible areas of the basement and crawl spaces for adequate insulation, I turned to the Building Envelop Research of the Oak Ridge National Laboratory for guidance. The Oak Ridge National Laboratory performs their Building Envelop Research for the US Department of Energy, DOE. The DOE publishes their guidance in their “Insulation Fact Sheet,” which is available on the blog home page. Following the recommendations by the Oak Ridge National Laboratory the attic, crawl spaces, eves, ductwork, underside of a large portion of the main level floor were insulated with cellulose. The pipes, wall end caps, knee walls, sump pumps and all identified areas were sealed, the garage ceiling was insulated and an insulated garage door installed. I was actually surprised at the winter energy savings and pleased with the improved comfort in the master bedroom and bath.

My next project was to spend the winter saving money eating and entertaining at home, watching DVDs for “nights out” on my LCD, eliminating trips to the mall and saving up money for my next energy saving project. Back in October 2008 President Bush had signed the Emergency Economic Stabilization Act of 2008 (P.L. 110-343). The Act extends the 30% investment tax credit for residential solar Photovoltaic or geothermal heat pump installation for eight years through December 31, 2016 and removed the cap on qualified solar photovoltaic projects and geothermal projects (from the previous $2,000). This allows taxpayers to use the credit to offset dollar for dollar their federal tax liability, and to carry unused credits forward to the next succeeding taxable year. Essentially Uncle Sam was now willing to pay 30% of the cost of my next energy savings project. I couldn’t believe it.
According to the DOE heating and cooling account for 56% of the energy use in a typical U.S. home, making it the largest energy expense for most homes. So that is where I looked for my next project. A wide variety of technologies are available for heating and cooling your home, and they achieve a wide range of efficiencies in converting their energy sources into useful heat or cool air for your home. Heat pump systems provide both heating and cooling and offer the benefit of delivering more useful energy than they consume. Unfortunately, on very hot days or very cold days they do not do as effective a job as an air conditioner and a furnace. For climates with moderate heating and cooling needs, heat pumps offer an energy-efficient alternative to furnaces and air conditioners.

Higher energy efficiencies are achieved with geothermal (ground-source or water-source) heat pumps, which transfer heat between your house and the ground or a nearby water source. Although they cost more to install, geothermal heat pumps have low operating costs because they take advantage of relatively constant ground or water temperatures. However, the installation is expensive because of the need to bury coils to deliver constant temperature fluid or install a groundwater pump and injection well to supply constant temperature water to the system. Ground-source or water-source heat pumps can be used in more extreme climatic conditions than air-source heat pumps, and are more effective at cooling and heating at the extremes.
According to the heating and cooling experts and the manufacturers of the various equipment that I have, my heating and cooling system, which is a split system with a gas furnace and air conditioner for the lower level and an air heat exchanger for the upper level, should last another 7-12 years. The most sustainable approach would be to use the current system for its entire expected life despite the fact that I could probably reduce my energy consumption somewhat by changing from my current equipment to two geothermal (ground source) heat exchangers. Though geothermal heat exchangers are more expensive to purchase and install than a traditional furnace and air conditioner, they are far more efficient, reportedly consuming 25-30% less energy to operate. The most reasonable thing to do was to wait and continue using my current system even with availability of the tax credit. Thought for the next several years I will continue to keep an eye on my equipment condition.

In October 2009 Virginia announced that a portion of the stimulus dollars for the state would be allotted to its Residential and Commercial Solar and Wind Incentive Program to provide rebates to partially reimburse the costs of renewable energy systems. For residential users on the first 10 kilowatts, the rebates will be $2.00 per watt for Photovoltaic Solar systems, $1.50 per watt for small wind turbines and $1.00 per watt for solar thermal units (solar hot water heaters). The rebate is less than you might think because system capacity is defined as the installed system’s predicted peak alternating current (AC) output which is around 75%-80% of the DC rating. Combining this incentive with the federal tax credit of 30% and the sale of the renewable energy credits, REC’s, which can be sold to utilities needing RECs and suddenly, there is a positive return on the investment. It was still a big decision because even with rebates and tax credits we have to come up with the cash to pay for the system and while current prices quoted for RECs are $220-$300 per kilowatt/year and are sold in 4 or 5 year contacts there is no guarantee that the REC’s will have any value in the future.

One of the selection criteria for my home was the large southern roof span, perfect for solar panels. I was able to reserve funds from the Virginia Renewable Energy Rebate Program for a 6 kilowatt solar photovoltaic system before all the money was gone and we put the deposit down for an American made solar photovoltaic system installed by a local company. We will be installing a 6 kilowatt system that we estimate will save us approximately $1,300 per year on our electric bill. That is about twice the savings we achieved by insulating the house; however, the cost (before rebates and incentives) is more than ten times the cost of the insulation project. Even after all the rebates and incentives (assuming I successfully navigate these) this energy savings was many more times more expensive than the insulation project.

Geothermal Heat Pumps

The most effective type of heat pump is the geothermal heat pump, GHP. It doesn't create heat by burning fuel, like a furnace does. Instead, in winter it collects the Earth's natural heat through a series of pipes, called a loop, installed below the surface of the ground or submersed in a pond or lake. As you may have experienced in a cave, the temperature six feet beneath ground surface is cooler in summer and warmer in winter than the ambient temperature. Using this temperature as its source the GHP can operate within its most efficient range. In winter, fluid circulates through the loop and carries the heat to the house. There, an electrically driven compressor and a heat exchanger concentrate the Earth's energy and release it inside the home at a higher temperature. Ductwork distributes the heat to different rooms. In summer, the process is reversed. The underground loop draws excess heat from the house and allows it to be absorbed by the Earth. The system cools your home in the same way that a refrigerator keeps your food cool by drawing heat from the interior, not by blowing in cold air.

The geothermal loop that is buried underground is typically made of high-density polyethylene, a tough plastic that is extraordinarily durable but which allows heat to pass through efficiently. The fluid in the loop is water or an environmentally safe antifreeze solution that circulates through the pipes in a closed system. Earliest systems were open loop, but those could impact the groundwater supply and are not used as much today. There are two types of closed loops used to provide constant temperature to the GHP. Horizontal ground loops are usually the most cost effective when trenches are easy to dig and the size of the yard is adequate. Workers use trenchers or backhoes to dig the trenches six feet below the ground in which they lay a series of parallel plastic pipes. They then backfill the trench. Fluid runs through the pipe in a closed system. A typical horizontal loop will be 400 to 600 feet long for each ton of heating and cooling.

The vertical loop is used where there is little yard space, when surface rocks make digging impractical, or when you want to disrupt the landscape as little as possible. Vertical holes are typically 150 to 450 feet deep and contain a single loop of pipe with a U-bend at the bottom. Each vertical pipe is then connected to a horizontal underground pipe that carries fluid in a closed system to and from the indoor exchange unit. Vertical loops are generally more expensive to install, but require less piping than horizontal loops because the Earth's temperature is more stable farther below the surface.

Geothermal heat pumps (GHPs), more accurately called ground-source heat pumps, have been proven capable of producing large reductions in energy use and peak demand in buildings. Although the U.S. was once the world leader in GHP technology and market development, European markets now absorb 2 to 3 times the number of GHP units annually as do the U.S. domestic markets. In 2007 the Intergovernmental Panel on Climate Change identified the building sector as having the highest green house gas emissions, but also the best potential for dramatic emissions reductions. In their report GHPs were specifically identified as a solution that is economically feasible under certain circumstances‖ in continental and cold climates. Their report cited cases where total electricity use decreased by one third and heating energy use by 50 to 60 percent.

Tax credits for home and business owners investing in GHP systems were enacted in October 2008 through 2016 and increased in the stimulus plan of 2009. Hopefully these tax credits will help GHP achieve wider market acceptance despite its large upfront capital costs. The largest hurdle to the widespread adoption of GHP technology seems to be the capital cost for initial installation. The outside portion of the GHP system can be half or more of the overall GHP system cost (and equal to the total cost for a traditional furnace and air conditioner). The technology while economically viable, is little known or understood and has suffered from the high upfront and installation costs. If the costs of the exterior coils were excluded, GHP systems have about the same price as competitive alternatives. In addition, due to the lack of demand, there are few design and installation firms in the market.

Buildings, both residential and commercial, account for about 40 percent of primary U.S. energy consumption, 72 percent of U.S. electricity consumption, 55 percent of U.S. natural gas consumption, and significant heating oil and propane consumption in the Northeast. While industrial use of electricity has been flat for about 15 years, electrical use to power commercial and residential building has grown by more than 50 percent since 1985. U.S. resources and investment have been deployed to build the infrastructure required to generate, transmit, and distribute electricity to serve that growth. Reducing the peak electricity demands for air conditioning and heating could alleviate peak demand on the electrical grid. Buildings present one of the best opportunities to economically reduce energy consumption and limit green house gas emissions. A recent study by McKinsey & Company study performed for the Department of Energy found that reducing the consumption of energy in buildings is the least costly way to achieve large reductions in carbon emissions.

A study by the U.S. Environmental Protection Agency (EPA) comparing the major HVAC options for residential applications determined that GHPs were the most energy efficient and environmentally benign option. Yet only about 60,000 units are installed each year in the combined new built and retrofit market. This languishing of the market is attributed to several federal policy lapses. A program at the DOD ran for several years in the late 1990’s intended to increase use of GHPs in federal buildings. This program’s authority was allowed to lapse. Although DOD took the initiative to restore the program 14 months later by then much of the GHP project pipeline had diffused away. A second policy mistake damaging to federal agency use of GHPs occurred in 2005 when the Energy Policy Act defined renewable energy that counted toward agency renewable goals as power generation only, excluding thermal forms of renewable energy such as GHPs. No lobbyists were paid to identify this oversight. Federal utilization of GHPs might have created the critical mass for the market; instead it was once more forgotten.

The basics of GHP technology have changed very little over the decades but awareness, understanding, and acceptance of the systems is limited. The systems are truly misnamed, GHPs are often confused with geothermal power production, in which the extreme heat of subsurface geological processes is used to produce steam, and ultimately to generate electricity. GHPs are also sometimes confused with the direct use of geothermal heat in which greenhouses, aquaculture ponds, and other agricultural facilities are heated using lower-temperature sources such as hot springs. Ground source heat pumps can be used economically anywhere and utilize the earth stored solar energy to function. There are at least 16 manufacturers of GHPs in the United States that participate in the residential and commercial markets. The GHP market began to develop in the late 1970s, and has had its ups and downs due to the cyclic nature of the buildings industry and volatility in government and utility support and the prices of competing forms of energy. The current tax incentives and awareness of US energy consumption may serve as an opportunity for the GHP market to achieve critical mass.

Carbon Footprint, Carbon Savings and Carbon Offsets

All resources are finite. As humans our resources consist of money, time, passion and energy. In the end, where, how and when we deploy these resources will determine our comfort and happiness with our lives. While there are some basic truths, the optimal allocation of your resources is based on your values and goals. We all should be thoughtful in our living, smarter about the ways in which we use the earths and our personal resources.

According to McKinsey and Co. it cost an additional $30-$40 above normal energy production costs to eliminate one ton of CO2 emissions by replacing traditional energy production with solar or wind power (the presumed life of the equipment was unreported). However, when a ton of CO2 was saved using LED light bulbs or energy-efficient appliances money was also saved ($108-$159 less was spent on energy for every ton of CO2 saved). The costs associated with generating power without CO2 emissions are higher than current costs. If the money is spent to reduce CO2 by replacing generating capacity there will be less money to spend on other things that matter to you or are necessary for your life, but if you reduce the use of energy less money is spent on energy and more money is available for other goals.

When you use less energy, by insulating, changing to lower energy light bulbs, controlling passive solar heat, or using energy star appliance, less energy is used, less CO2 released and money is saved. Reducing your energy consumption is a far better utilization of resources. While solar panels and wind turbines are sexy, and renewable sources of energy sound wonderful, these technologies are still in their infancy. Geothermal generation of heating and cooling and nuclear generation of power have failed to catch on in the United States, but have advanced significantly in the past few decades in overseas locations. Conservation and energy efficiency are currently well developed technologies, effective and relatively cheaper. Use less so that we can all live within the productive capacity of the existing infrastructure. Then only expand the generating capacity in ways that do not release CO2, do not burden the earth.

Adding insulation and sealing existing homes and commercial buildings is by far the low hanging fruit and a good source of “green economy” jobs. The Wall Street Journal reports that heating and cooling buildings account for about half of the CO2 emissions in the U.S. My home was built in 2004 and is heated and cooled with a duel system; the upstairs with an air heat pump and the lower levels with a gas furnace and air conditioner. Replacing the heating and cooling systems with geothermal systems would only make sense when the existing systems reach the end of their functional life. After eliminating incandescent light bulbs, upgrading all appliances to energy star, installing reflective films on the window and installing drapery, I found that adding insulation was a good way to further reduce the energy consumption of the house. Following the recommendations of the Building Envelope Research of the Oak Ridge National Laboratory the attic, crawl spaces, eves, duct work, underside of a large portion of the main level floor were insulated with cellulose. The pipes, end caps, knee wall, sump pumps and all identified areas were sealed, the garage was insulated and an insulated garage door installed. After six months electricity usage (as measured in kilowatts for the same six months the previous year) had been reduced by over 6% (despite relocating our workspace to the home with all its attendant equipment) and the winter liquid propane usage (as measured in volume use December through March both years) was reduced by 25%. Also, the overall comfort in the bedroom over the garage and the master bedroom has been vastly improved. I was very surprised (and pleased) at the energy savings for what was a well insulated home.

Though I do not need to commute to a job, I still drive my (gas hybrid car) almost 4,000 miles a year. The hybrid does not make economic sense especially because I drive so little. However, it does make me happy to drive so to me it was worth the extra money I paid for it. In searching for the carbon emitted per vehicle mile I could only find the 1993 data from the Nowak study which lists 0.88-1.06 lbs CO2 per mile. This is probably high for my hybrid, which was not available at the time of the study. The same article states that each person in the US generates 2.3 tons of CO2 each year, which appears in conflict with the automobile numbers until you realize that babies and children do not have cars and city dwellers automobile ownership and use is also much less than suburban use. During the eight years I lived and owned a car in the city, I drove less than 1,000 miles a year. After reducing the energy use in my home, eliminating commuting from our lives, reducing frivolous travel I still wanted to do more.

I found the following fact: “A single mature tree can absorb carbon dioxide at a rate of 48 lbs/ year and release enough oxygen back into the atmosphere to support 2 human beings.” The Tree Folks are the source of the above information, and are willing to sell carbon off-sets in the form of trees. I tend to think of carbon off-sets for people who want to vacation in Bora Bora or have the wedding or Oscar party of the century, but in truth they are probably for people like me who use various technologies to make their lives richer and happier. My large house comes with a big piece of land. Admittedly, most of the land is wooded undisturbed land and part of the Chesapeake Bay water shed, but I do have about 3 acres of mostly open land around the house. We planted 43 trees of moderate maturity (over 6 foot each). Using the Tree Folk data, forty-two trees absorb a ton of carbon a year and the last tree replaces a diseased tree we cut down. Beyond watering the trees in the first three weeks they were planted, they have thrived on benign neglect. I am already drawing up plans, researching native trees, and saving my nickels for another 3.6 tons of annual carbon off-sets otherwise know as another 150 trees. I may have to make that 152 trees because there are two more existing trees that are not doing well.

Trees can also reduce air conditioning and heating needs by providing shade and providing a wind shield for winter. Trees also act as natural pollution filters. Their canopies, trunks, roots, and associated soil and other natural elements of the landscape filter polluted particulate matter out of the flow towards the water shed and use nitrogen, phosphorus and potassium which are contributing factors to the decay of the Chesapeake Bay water shed. Trees are pretty.