You’ve no doubt been hearing more and more about carbon emissions and may wonder what it means. You may even be curious about how to measure your contribution to the humanity’s collective carbon footprint. Simply stated, carbon emissions is the sum of carbon dioxide (CO2) generated by society’s use of fossil fuels like oil, coal, and natural gas which, when combusted to produce energy, ends up in the atmosphere.

Carbon dioxide in the atmosphere is absolutely essential for life. All plants depend on it. They take it in through respiration and use it to produce the carbohydrates that we eat either directly or indirectly as part of our diets. The plants also convert CO2 to produce the oxygen we breathe. The problem with CO2 is that its atmospheric concentration has been increasing steadily starting around the time we began using fossil fuels that previously had been sitting there buried for millions of years. The atmospheric concentration of CO2 has gone up by about 25% in the past 50 years and since CO2 acts as a greenhouse gas by trapping heat, there is a legitimate concern that it may change the climate to a point where the earth may undergo a positive runaway effect, triggering another mass extinction event. I know that there is some debate about this issue, but the consequences are so dire it’s really not worth arguing about anymore. Combined with the inevitable depletion of fossil fuels, it means we must find alternatives to replace the energy society uses on a daily basis and the sooner we can do it, the better off we’ll be.

There are a number of websites with carbon calculators that try to accurately compute an individual’s carbon footprint. An individual carbon footprint is the amount of CO2 a person’s activities generate on an annual basis. The easiest way to estimate an individual carbon footprint is to look up your country’s per capita number on the Internet and assume yours is in that range. But if you’re curious how to you might modify your own personal carbon footprint, the calculator may be helpful, particularly if it explains the methods it uses to compute its values.

In the case of U.S. residents, our country’s annual CO2 emissions are 6 billion metric tons (13.2 trillion pounds). Divide that by our population of around 300 million and you get 20 metric tons per capita per year (about 44,000 lbs. per capita). I began to wonder where all that CO2 allocation was coming from and if there’s anything I could do to reduce my contribution to it. By the way, Americans have a much higher carbon footprint than most other countries and significantly more than third world countries. There are some who feel that we should be profoundly ashamed of our lifestyles and that we need to get our carbon footprint aligned with that of the rest of the world. In the meantime, some of the countries with the lowest per capita carbon footprints are desperately trying to get their lifestyles to more closely match ours which will have the effect of increasing world carbon emissions overall.

The largest personal carbon contributors are due to household energy use and transportation. Depending on the website you use, it will ask questions such as the state where you live, the size and age of your home, the type of vehicle(s) you drive, your annual mileage, and many other questions. I wanted to know more about the assumptions that were made and so after doing some of my own research, I came up some simple rules of thumb. They involve converting one’s energy consumption into BTUs and then converting BTUs into CO2 emissions depending on their carbon source. Otherwise, you may not know how clever the calculator is trying to be with all the questions it’s asking. For example, if you live in a state that gets most of its electricity from hydropower like Idaho does, you may get a reduction on your electrical carbon contribution, which isn’t quite right since electricity works a bit like a shared resource whose carbon emissions should be recognized by the combined sources of electricity on a national basis.

I like to use British Thermal Units (BTUs) to measure thermal energy. BTUs have more meaning to me than the metric units for energy like calories or Joules. A BTU is defined as the amount of energy required to raise one pound of water 1 degree Fahrenheit. The equivalent unit in the metric system is the calorie, which is defined as the amount of energy required to raise one gram of water 1 degree Celcius. The calorie such a small unit of energy that almost no one uses it. You may think that it’s used to measure food energy, but it’s not. A food calorie is actually 1000 thermal calories. In fact, it is really a kilocalorie (kcal). But for simplicity’s sake, everyone just calls it a ‘calorie’. Can you see a problem there? I sure can. Getting calculations wrong is very easy when you use the same name to refer to vastly different amounts of energy. For example, I once was reading a book called Games for the Super Intelligent and in the book the author calculated that the ice in each Scotch and soda he drank required his body to raise the temperature of the drink, presumably at 32F, up to his body’s internal temperature. He reasoned the energy his body needed to do that would more than offset the calories in the Scotch and soda. He should have been able to lose weight like mad with each and every drink. He tried it and concluded it didn’t work. It would have, but only if he had increased the ice water by a factor of 1000. Imagine drinking 50 gallons of ice water with each 7 oz. Scotch and soda! That would certainly require your body to work overtime to maintain a normal core temperature. So even people who are super intelligent can get tripped up by the food calorie vs. thermal calorie confusion. I find it best to stick with BTUs, because they only have one meaning.

The metric system can be pretty convenient when you don’t have a calculator because everything is expressed in powers of 10. However, once you bring in calculations that involve time or energy, much of the mathematical elegance falls apart, and you’re not much better off than any other system. So that’s why I don’t mind using the antiquated, yet convenient, British system when discussing energy. You’ll also notice that the world uses other non-metric units when discussing energy such as barrels for oil (which are 42 gallons each) and cubic feet for natural gas. So it’s pretty hard to get away from having to know all the conversion factors when dealing with energy. Fortunately, in the U.S., we are multi-lingual when it comes to measurement systems out of necessity. I’m just thankful I don’t have to know 4 languages like many of our friends in Asia and Europe need just to get through the day.

It’s pretty easy to get the values for BTUs since most fuels have pretty well-established BTU ratings. In fact, in the U.S., items like fuels and furnaces are more likely to be specified by their British system ratings than their metric equivalents.

Here are some common BTU ratings for typical fuels:

Ethanol 84,000 BTU per gallon
Gasoline 124,000 BTU per gallon
Jet Fuel 134,000 BTU per gallon
Natural Gas ~ 1,000 BTU per cu. ft.
Wood 7,000 BTU per lb. (average)
Coal 10,000 BTU per lb. (average)
Garbage 5,000 BTU per lb. (average)

I then did some calculations based on this data that allowed me to convert BTUs into lbs of CO2 emissions using these conversion factors:

Coal/Wood ~ 1 lb of CO2 generated per 5000 BTU
Oil/Gasoline ~ 1 lb of CO2 generated per 6500 BTU
Natural Gas ~ 1 per lb of CO2 generated per 8700 BTU

Once you know how much of each type of energy you use, you can more accurately determine its effect on the overall carbon footprint. Incidentally, I included wood only for comparison’s sake in the list above. If you use wood for heating, you get a pass on CO2 emissions because it’s only ancient carbon we’re worried about. However, if your wood burner is stinking up the neighborhood and stinging your neighbors’ eyes, you might want to keep your smug factor down to a minimum. 🙂

The best way to compute gasoline consumption is by knowing how many miles you drive each vehicle per year and the fuel economy of the vehicle. The U.S. average distance per vehicle per year is around 12,000 miles and the average fuel economy is around 25 mpg. So knowing those two numbers, an average car’s carbon footprint can be computed with this equation:

12,000 miles / 25 mpg x 124,000 BTU/gal x 1 lb CO2/6500 BTU = 9,156 lbs of CO2/yr

Similarly, a typical 2100 sq. ft. Colorado home uses about 90 MBTU for home heating per year and so dividing that by 8700 BTU/lb, assuming natural gas, which is the most common heating fuel in Colorado, gives 10,344 lbs of CO2/yr. for home heating.

Flying can also contribute significantly to one’s carbon footprint. A commercial jet effectively gets about 42 passenger miles per gallon so you can figure out if you fly 4 trips totaling 12,000 miles per year, the CO2 generated due to that activity would be 5890 lbs of CO2. Please note that the maximum theoretical values for fuel economy with public transportation are rarely reached due to capacity factors. Modern airliners can get 60 passenger miles per gallon if they are 100% full and fly only long routes, but 42 passenger mpg is closer to the average fuel economy.

To get the contribution for electricity, I used the fact that 30% of the electricity produced in the U.S. is from non-CO2 generating sources, primarily nuclear and hydroelectric and a small, but growing, amount from renewables like wind, solar, and biomass. The other 70% comes from burning fossil fuels.

A coal plant has about a 33% thermal efficiency and coal accounts for 50% of the electricity in the U.S.. One kWh of electricity is equivalent to 3412 BTUs and dividing that by .33, I get 10,236 BTU of coal to generate a kWh of electricity. Using my conversion factors above, it means a typical coal plant generates about 2 lbs. of CO2 per kWh of electricity generated. Since coal accounts for 50% of total U.S. electricity production, I will use 1 lb. of CO2 per kWh as the average carbon contribution due to U.S. electricity generation from coal. Likewise, natural gas is responsible for about 20% of the electrical generation in the U.S., but it has better efficiency due to the fact that most of the gas-generated electricity uses combined cycle and it also generates less CO2 per BTU and so its overall contribution is about .2 lbs of CO2 per kWh. Some electricity is also generated by oil but it’s down to less than 2% of the total and declining, so I’ll ignore that contribution because it doesn’t affect the overall picture very much. This means that the fossil fuel contribution in the U.S. to electrical generation is about 1.2 lbs per kWh, on average. Since the average household energy consumption is about 8760 kWh per year, this adds another 10,512 lbs. of CO2 per household.

So, now I will add the major contributors to an individual’s CO2 footprint:

2 cars = 18,312 lbs
home heating = 10,344 lbs
air travel = 5,890 lbs
electricity = 10,512 lbs

Total = 45,058 lbs

CO2 per capita 11,264 lbs (assuming a family of 4) for electricity, heat, and transportation.

This only appears to add up to about 1/4 of the per capita number you get when you divide total U.S. CO2 emissions by its population. But I left off contributions due to food and other consumer items as well as energy used by commercial and industrial customers.

Food and consumer goods all include some amount of embodied fossil fuel energy. What I mean by that is that if I eat an apple, there is fossil fuel energy attributable to the apple grower, the trucking firm that delivered it, and the supermarket that sold it that is embodied in that apple and thus that energy should be attributed to my personal carbon footprint.

The food to sustain a human for a year, based on a diet of 2400 kcal/day is 876,000 kcal per year. There are 4.2 BTUs per food calorie so this is equal to 3.7 MBTU. However, the carbon content of food is based on recent CO2 absorbed into plants. So this CO2 would not count toward CO2 emissions from ancient carbon in fossil fuels, which is what we’re trying to measure here. However, some studies have found that every food calorie produced in the U.S. requires about 10 kcal (42 BTUs) of fossil fuel energy. So if you look at it like that, then you would get another 37 MBTU of embodied fossil fuels due to food consumed per person per year. This would add about 5500 lbs of CO2 per capita due to food. For that calculation I used an average of 1 lb. of CO2 per 6700 BTUs to give the embodied fossil fuel energy in food an average somewhere between coal, oil, and natural gas. This was a real eye-opener for me. I had assumed that my car consumed significantly more fossil fuel that my body did, but the number is only a factor of 2 higher for my car or my furnace compared to my body, if you take into consideration that the 10 x multiplier effect of food on fossil fuel energy. Not all food calories embody the same about of fossil fuel. It ranges from about 3 x for some foods to 35 x for meat according to that study. This is why many of the on-line CO2 calculators will ask how often you eat meat or whether you buy organic foods. I will reserve judgment on whether this embodied fossil fuel energy in food is accurate since many people unknowingly quote a study by Pimentel that corn ethanol takes more fossil fuel energy to produce than it provides as a fuel, and that study has been contradicted by every other researcher on that topic. Not surprisingly, the studies that allocate 10 kcal of fossil fuel per kcal of food extensively quote Pimentel’s publications.

I had done calculations many times in my head and had been ignoring the value due to food because I knew intuitively that the daily consumption of 9600 BTU of food is equivalent to about a pound of coal, and that is only about 1 kWh ($.10) of electricity which is tiny compared to the amount of energy we use for household electricity and heating. I hadn’t really thought that food could have impacted my carbon footprint very much until I considered the embodied fossil fuel energy in it. Similarly, you can imagine that the energy required to produce other items we use daily such as clothing, furniture, appliances, etc., all have some contribution from fossil fuels.

It’s also important to realize that after the kids are grown and move out of the house, it becomes a household of two adults, and the per capita energy consumption goes up proportionally. The tendency for fewer people to live in ever-larger houses is also causing per capita carbon emissions to rise as well.

To figure out where the rest of the per capita energy comes from, there are other energy consumers such as retail stores, private industry, schools, government offices, etc., whose energy consum
ption all gets allocated to each U.S. citizen.

So what did this exercise show me? It showed me that to significantly reduce my carbon footprint to a level where I should no longer feel shame and guilt, I should grow my own organic food, live in an unheated hut (probably closer to the equator), use wood and dung for cooking, and get rid of my car. In other words, I would need to swap my lifestyle with someone who lives in a third world country. Actually, “swap” isn’t really a good term to use, since if I simply swapped lifestyles with someone else in the third world, the person who got my house would likely want to keep it heated and use the electric appliances, cars, etc., so that wouldn’t work. Instead it would be better if I dismantled my house and buried it or recycled it along with the cars, and let the prairie re-grow in its place. It sounds a little absurd, but there are some who think that is the correct approach.

I’ve already written about the difficulty of trying to substantively cut carbon emissions with minor steps like replacing incandescent bulbs with CF bulbs. To make a real difference in a carbon footprint, we’ll need to cut consumption by significant amounts and at the same time start generating more of our energy with renewable sources. Can it be done? I think it can. But I’ll leave that for a future posting.

I’ve been using compact flourescent lights in my home for a few years and feel like I’m ‘doing my part’ to help save the planet. My wife assures me that I’m being an exemplary ‘Treehugger’. I purchased these bulbs on my own without any inducement to do so other than curiosity. But I recently heard that some misguided do-gooders are trying to outlaw incandescent bulbs. Even though that might not affect me too much since I’m already ‘with the program’, so to speak, I’m not a big fan of government intervention, unless it’s for a really good cause and unless it can be proven to solve a problem without introducing some other unintended consequences.

Not everyone is ‘on board’ when it comes to CF bulbs. A friend had asked me whether CFs light bulbs really have much of an impact on global warming by reducing the amount of CO2 that our fossil fuel-powered electric plants spew into the atmosphere each year. He wondered whether anyone had taken into account the beneficial effect of the heat incandescent bulbs generate in the winter time that offsets the load on the residential furnace. I had to admit, I had never heard of anyone who had taken that into consideration. So I decided to do some calculations myself.

An incandescent bulb converts only about 2% of the input power in usable light. A CF bulb produces about 4 times as much usable light per watt than an incandescent light bulb. At this point, if I were on the usual trajectory of discussing energy savings, I’d be ready to start gushing about the number of tons of CO2 that could be avoided if everyone were all to switch to CF bulbs. But I’m not going to do that because talking about tons of CO2 doesn’t really tell anyone anything. Why even bring up the CO2 number at all? It really boils down to how much of a percentage impact you can have on a problem. Mixing pounds or tons of CO2 reduction when talking about energy efficiency is a complete non sequitur and does nothing to put energy savings in perspective. If I can tell you how much of a percentage savings you can expect with CF bulbs, then you can tell if it’s a big deal or a little deal and draw your own conclusions about its impact on CO2 reductions.

If an incandescent bulb is 2% efficient at converting electricity to light and a CF bulb takes about 25% of the energy to produce an equivalent amount of light, then it follows that it’s about 8% efficient. So, you might ask, where does all that other energy go that is not being converted into beautiful lumens of light? The answer is that it is converted into heat. Actually, even the lumens of light also end up as heat too, which means that after it has bounced around the room a few times, all the objects, including your retinas eventually turn those lumens into heat as well.

As you move away from the equator it’s necessary to use more interior lighting in the winter than in the summer due to the fact that the nights are longer in winter. If we need to use our lights longer, and all the energy used by the bulb eventually becomes heat, it begs the question, “Are these lights helping to offset the amount of work my furnace has to do?” For about 6 months out of the year my furnace runs at least a little bit each day, so yes, you can assume that the heat generated by my lights, and for that matter, my refrigerator, TV, computer, etc., all help to offset the amount of work that my furnace would otherwise have to do to keep my house at a comfortable temperature.

It would only be fair to acknowledge that in the summer, the opposite would be true, i.e., all my electrical loads counteract the work that my air conditioner needs to do during the time I’m running it.

But the winter months are when a typical house consumes most of its energy primarily for space heating needs. So, how much ‘help’ does my furnace get from my lighting, and how does it offset the cost of heat when compared with the cost of natural gas that handles the bulk of that task?

In a previous article I wrote for another website, I showed the effective cost of producing 1M BTUs using various fuels based on current prices and conversion efficiencies. There is a table in that article that shows that natural gas effectively costs about $14 per MBTUs based on a furnace with 85% efficiency. For a similar amount of energy from electric resistive heat, which is 100% efficient, the cost is about $26 per MBTUs assuming a $.10/kWh electricity cost.

A typical household in the U.S. uses electricity at the rate of 1 kW. This results in an average electric bill that is 720 kWh per month or 8760 kWh per year. You can multiply those numbers by $.10/kWh to figure the monthly and yearly average cost of electricity in the average U.S. household. Please note that U.S. kWh rate varies considerably by geographic area from as little as $.06/kWh to $.25/kWh with the average being around $.10. Prior to the widespread use of CFs, about 9% of residential electricity consumption was attributed to lighting according to the U.S. Department of Energy’s website. Since heating values are typically measured in BTUs (at least here in the U.S.) I will convert the electricity used for lighting into heat using the standard conversion factor of 3412 BTU/kWh. It gives a value that the lighting load in an average residence of about 7400 BTU/day. In the winter, we can assume this is higher, and in the summer, it would be lower due to the difference in the length of the days. I will use 10,000 BTU/day for winter months and 5,000 BTU/day in the summer for simplicity’s sake.

A typical household in the U.S. uses about 90 M BTU per year for space heating and most of it is consumed during 4 months in the winter. That would be a heating load of 750,000 BTU/day on average. This means that a typical furnace consumes about 75 times as much energy during the winter as all the lighting in a house. Heat generated by lighting will thus offset the furnace load during the winter months by about 1.3%.

In the summer, the heat load that lighting generates will need to be offset by the air conditioning, and thus will increase air conditioning cost, and using the numbers from the same DOE website shows that 16% of annual electricity consumption attributable to air conditioning. In the event that all 16% of the air conditioning bill was generated during 4 months in the summer then the monthly average consumption would be 350 kWh during those months. This corresponds to 12 kWh per day. Using a conservative SEER of 10 means 12 kWh translates to cooling of 120,000 BTU/day. (See my article on Heat Pumps for the definition of SEER and other efficiency ratings.) With the 5000 BTU/day of heat generated by lighting in the summer, the air conditioner has to work 4% harder to compensate for the heat generated by the lights.

So, what are savings associated with compact fluorescent lights? Assuming you can cut down on the thermal heat generated by 75% over incandescent lights, which, as I mentioned average about 9% of a typical electric bill, you should be able to save about $59/year in electricity if you could convert all your lights to CFs. This amount comes from a calculation of:

.75 x 8760 kWh/year x .09 x $.10/kWh = $59.13

You’d have to buy about 1% more natural gas to compensate for getting 75% less heat from CF lighting in the winter. This will cost an extra $12.60. (.75 x .013 x 90 MBTU x $14.00/MBTU)

In the summer, you’d get a 3% break on your air conditioning bill which, using $.10/kWh, would come out to $4.20 annually. (.75 x .04 x .16 x 8760 x $.10)

CF bulbs are more expensive to purchase than incandescent bulbs, about $1.50 vs. $.50 each for a 60W bulb. But they last about 8 times longer, so even with the higher purchase price, you will spend 63% less per bulb replacement cost overall. Again using the 9% of an electrical bill over a year, the lighting consumption comes out to an average of 788 kWh per year. That’s like having 1.5 60-watt incandescent bulbs burning all the time. If you did that, each light would need to be replaced about 8 times per year (assuming an 1100-hour life) for incandescent bulbs vs. 1.5 times per year with CF bulbs (assuming an 8800-hour life). So the bulb replacement cost savings are an additional $1.75/yr.

The calculation I used for that was:

8 incandescent bulbs x $.50/bulb – 1.5 CF bulbs x $1.50/bulb = $1.75

So lets add it all up:

$59.13 +$4.20 + $1.75 – $12.60 = $52.48 annual household savings to going to CFs

So it appears that the electricity savings + reduction in air conditioning + reduced in cost of replacement bulbs – loss of heating in winter still makes it more economical to use CFs over incandescent bulbs. It’s interesting to note that the savings in electricity is by far the dominant contributor to the savings calculation.

But in the grand scheme of things, a reduction of $52.48 in a combined heating + electricity bills of around $2100 annually is less than a 2.5% household energy savings and thus isn’t going to make a big dent in global warming or reduce our dependence on fossil fuels very much.

It would seem that passing a law to make incandescent bulbs illegal is just something to make people who are unable to do math feel good about themselves. Maybe they can express it in tons of CO2 savings and obfuscate its contribution even further. Let’s just call it what it is, a potential 2.5% energy savings which is not nearly enough incentive to pass a law when the simple economics should provide enough of incentive, not to mention cutting one’s bulb replacement workload down by 87%.

Now I know that some may want to take me to task for my criticizing CF bulbs for making minimal contributions to the goal of overall energy reduction, but I am a tired of people saying things like, “But if everyone just did a little, we’d save a lot“. No, we really wouldn’t. If all 100 million households in the U.S. save 2.5% of their electricity bill by switching to CFs, the overall savings are not 250,000,000%, as some math-challenged people may think, they are just 2.5%, overall, period. Savings like this would get eaten up in about 3 years with a population increase which is occurring at nearly 1% per year in the U.S..

I wish that everyone would just talk in terms of percentages when it comes to reducing energy consumption and not obfuscate the issue by introducing tons of CO2 emissions or some other unrelated metric into every energy discussion. One of my favorites is using an seemingly impressive expression such as ‘equivalent to taking 100,000 cars off the road’. Just to put that in perspective, there are 600 million motor vehicles in the world, so, although 100,000 sounds like an impressive number, it’s less than .01 percent of the total. Just in case there’s any doubt, I consider a .01 percent improvement to be a insignificant contribution that is hardly worth talking about. So I think we should stick to percentages when it comes to energy improvements.

To eliminate modern society’s dependence on fossil fuels, we will need to find ways to significantly reduce energy consumption as well as simultaneously figure out how to augment and eventually replace nearly all of our current energy production with renewable energy sources. I don’t think we can legislate a solution into existence by targeting small contributors like residential lighting. If we want to be a good “energy efficiency fascists” so as to modify people’s behavior with legislation, then we’ve should be attacking energy consumption on a larger scale while simultaneously replacing massive amounts of generating capacity with renewable sources. A 2.5% reduction that already has an economic incentive would be unlikely to benefit from further legislation to outlaw incandescent bulbs. Besides, there are some applications that incandescent bulbs can do where CF bulbs would not work well, such as lighting the inside of a refrigerator. CFs take about a minute to warm up and so a refrigerator is much better served with an incandescent bulb. It’s only on when the door is open, after all.

I guess I should also mention the controversy of the mercury in CF bulbs. Mercury has been used in fluorescent bulbs ever since they were invented in the 1930s, and no one gave it much thought. Commercial and industrial lighting applications converted over to fluorescent bulbs years ago and have had methods for their proper disposal going back decades. The disposal method for a burned out CF bulb is to put it in a sealed bag and bury it in a landfill so that it doesn’t end up in our water supply. One source of methyl-mercury that ends up in fish comes from burning coal, which goes into the atmosphere, comes down in rain, and can concentrate in fish. Since CF bulbs require less electricity, hence less coal is burned to generate electricity, the overall effect of the mercury contamination concern is reduced with CF bulbs, but this is often neglected because of the hysteria about what to do if a CF bulb breaks, a topic that has been answered by the EPA.

So in conclusion, I think that CFs are a good idea that need no further government legislation to get them to be more fully adopted. There’s speculation that they may even be replaced with LED technology in the future which will eliminate the mercury concern, but I think that may take a while. I’ve been using a white LED for reading lamp and it is 1000 times more efficient than using a 60W incandescent bulb, but that’s mostly due to a behavioral change, since I’m lighting up just the reading material, not the whole room with the reading light. Those are the types of changes it will take to get off the fossil fuel gravy train. In reality, the number of lumens per watt for a white LED are only about 50% more efficient than CFs today. Even with the further LED technology improvements in the number of lumens per watt, it won’t be quite the 4x jump in efficiency that we made by going from incandescent bulbs to CFs, but perhaps another 2X improvement over CFs, which would be worth switching if they can get the multi-watt LED lamp costs to be competitive with CF bulbs. Today, for limited power requirements such as flashlights, the switch is already happening which is why you are seeing more and more flashlights switching to LED technology.

My friend Jack asked me recently about geothermal heat pumps. I have been looking into heat pump technology for a while and wanted to write about it, so I gave him a longer-than-usual reply and figured I’d put some of what I wrote in my blog for anyone else who was curious about ground source heat pumps and net zero homes in general.

Heat pumps are like air conditioners running in reverse. You can use a heat pump to either heat or cool a building by reversing the flow of its refrigerant. Just as air conditioners become less efficient when the outside temperature gets too high, heat pumps get less efficient when the outside temperature gets too low (like around 30F). Of course, this is the worst time for a heating system to start losing its efficiency, that is, as the outdoor temperature gets colder, because it’s precisely when the maximum output from it is required. This is one of the reasons heat pumps have not been as popular in colder climates as they are in mild climates.

However, despite these limitations in colder climates, advancements in technology have made air source heat pumps increasingly viable for a wider range of environments. Modern heat pumps are designed to operate efficiently even in temperatures below freezing, making them a more reliable option for year-round heating and cooling. By investing in a high-quality system from reputable air source heat pump suppliers uk, homeowners can ensure they are getting a unit that is optimized for performance and energy efficiency. This makes heat pumps a more attractive option for those looking to reduce their carbon footprint and lower their energy bills, even in less temperate regions. In addition to their improved efficiency, air source heat pumps offer several benefits that make them a smart choice for both new builds and retrofits in existing homes. These systems are easier to install than ground source heat pumps, as they do not require extensive excavation or drilling. This can significantly lower installation costs and reduce disruption to the property.

Furthermore, regular maintenance is crucial for ensuring the optimal performance and longevity of air source heat pumps. Homeowners should schedule annual check-ups with a qualified heating service provider to keep their systems running efficiently and to address any potential issues before they become major problems. This proactive approach helps maintain the unit’s efficiency, preventing unexpected breakdowns and extending its lifespan. HVAC Minneapolis professionals are well-versed in the unique challenges and requirements of air source heat pumps, offering specialized services that cater to the specific needs of homeowners in the region. Investing in a reputable service provider not only enhances the performance of the heat pump but also provides peace of mind knowing that the system is in capable hands.

By sourcing their units from reputable heat pump suppliers, homeowners can also take advantage of local expertise and support, ensuring that their systems are properly installed and maintained. As a result, air source heat pumps are becoming an integral part of the push towards net zero homes, providing a sustainable and cost-effective solution for heating and cooling.

The benefit of adding a geothermal source to a heat pump is that the heat exchange loop stays at a consistent temperature. This allows the heat pump to maintain its efficiency because the earth below the frost line at most latitudes in the lower 48 states stays at a consistent 50-60 degrees F year round. This constant source of temperature allows heat pumps to maintain a high ‘coefficient of performance’ (COP). The COP is similar in concept to an air conditioner’s SEER (Seasonal Energy Efficiency Ratio). Basically, the COP is a ratio of watts of electricity input to watts of heat output you get. A typical heat pump has a COP of around 3 if the difference between the indoor and outdoor temperatures is within about 40 degrees F. The less the temperature difference, the higher the COP and conversely, the larger the temperature difference, the lower the COP. A COP of 3 is like getting 300% efficiency compared with simple electric resistive heat which is 100% efficient. A 100% efficient heater has a COP of 1. However, when the outdoor temperature approaches freezing, a heat pump’s COP can drop down below 1, at which time a resistive backup heater takes over. The primary drawback of an air source heat pump is that just when you need heat the most, a heat pump starts to get much more expensive to operate due to the reduction in its COP. For geothermal (i.e., ground source) systems, the COP is closer to 3.5 all the time and so it doesn’t suffer from the problem with air source heat pumps that vary with outdoor temperature.

An air conditioner’s efficiency is measured by its SEER which is basically the COP averaged over a range of typical outdoor temperatures and multiplied by 3.413. Typical values for an air conditioner’s SEER are around 10-15 which corresponds to an COP range of 2.9 – 4.4 . It’s been improving over the past few years, mostly due to government mandates. In Japan, they are now producing heat pumps with COPs as high as 6.

To add a geothermal heat sink to a heat pump system, you need to bury the heat exchanger loop below the frost line. This can be done using a loop in a vertical bore hole or in a horizontal trench. In general, a ground source heat exchange loop for a typical house would be between 1500 to 2500 feet long depending on the size of the system, and buried at least 6′ deep. The costs to install the heat exchange loop are similar to those of drilling a well in the case of a vertical system, or digging a 6′ deep trench several hundred feet long and two feet wide. So the installation of the heat exchange loop can get quite expensive. If the loop is arranged in a coil in a trench, you need about 1 foot of trench length per every 4 feet of loop. As you can imagine, this would not be easy to do unless it’s done during the construction of the house and prior to any landscaping. Also, if anything goes wrong with the loop such as having a leak, it would be very expensive to isolate and fix the problem once it’s buried.

If heat pumps are 300% efficient, why doesn’t everyone use them? After all, a gas furnace is only abut 80% efficient. One reason is that generating electricity from coal, gas, or nuclear power is only about 30-40% efficient. As much as 2/3 of the thermal energy created at an electric power plant becomes wasted heat. So the overall savings due to the multiplicative effect of the heat pump are offset by the losses of converting the fuel to electricity back at the power plant, not to mention the losses of delivering energy over the electrical grid. That’s part of the reason that electricity tends to cost about 3 times as much per unit of energy as buying natural gas and burning it in a furnace to heat your house. The capital and installation costs of a geothermal heat pump system are also significantly more than a gas furnace (about $25K vs. $3K).

I currently spend about $800 per year to heat my home with natural gas and a similar amount on electricity. I figure if I were to use electricity and a geothermal heat pump for heat, it would cost about the same as what I currently pay for natural gas, but I’d have an extra $22K in capital cost for the heat pump over the cost of a gas furnace. Now, if I had a total solar electric home then it would make sense to consider a heat pump, but to do that, I’d need to have about 12 kW of solar panels installed on my roof (at a cost of $86K), based on my annual gas and electric consumption. Even with generous solar rebates (currently $4.50/W by my utility company, up to $45K) and the new solar tax credit just passed by the U.S. Congress (up to 30% of the net solar system cost) that could take my cost of the solar system down to around $29K. But it still would be hard to justify because of the additional capital outlay for the heat pump, bringing the system cost up to $54K.

To get to net zero energy with my existing home using PV solar and a ground source heat pump, it would take about $111K in capital expenditures of which $57K could be foisted off on to my fellow taxpayers and utility customers. But that’s still too expensive to justify it based on its economic return. It would take about $54K in personal expenditures to save $1600/year in utility bills. Ignoring the cost of financing a $54K expenditure, the amortization of the system would be $2700 per year assuming it needed to be replaced in 20 years. But if energy prices doubled, which is certainly possible, it would begin to look much more attractive. They’d need to quadruple for it to be attractive without subsidies.

Energy efficiency initiatives don’t get a lot of attention because most of them have negative economic returns. This is usually due to the low cost of energy in the U.S. which is about half of what Europeans pay due to higher energy taxes. However, if you use energy efficiency as a way to reduce capital costs of a renewable energy system, the picture is quite different, primarily because renewable energy capital expenses are so high. My electricity and heating bills are currently on par with the U.S. average. If I could figure out how to reduce them by 50%, it would allow me to reduce the size of a renewable energy system proportionally to be half the cost. This is usually when efficiency becomes a much more attractive proposition. Getting by with a 6 KW solar system for all our electric and heating needs would cut the previously mentioned $86K pre-rebate cost in half.

If energy prices go up significantly, and there’s good reason to believe they will as oil and gas production peak, you’ll likely see a lot more uptake in the technologies that help create net zero energy homes.