Category Archives: technology

Heat Pumps and Net Zero Energy homes

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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.

The Kindle

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My friend Peter cares deeply about climate change and so he includes a line at the bottom of all his emails that admonish the reader:

Please consider the environment before printing this document.

As a consultant to HP and prior to that, an HP employee for 24 years, I worry about the prospect of people no longer printing out documents on paper and depriving HP of the profits that come from selling ink cartridges. But I can certainly understand Peter’s sentiment since, with the exception of photos, much of what’s printed ends up as trash a short time later. The same happens with newspapers and magazines. For me, books create another problem. I tend to hang on to many of my books after I’ve read them just in case I want to re-read them or refer to them in the future and this requires finding space to store them all. And it doesn’t help that I read books on an intermittent basis, sometimes abandoning a book half way through only to pick it up a few months later to finish it and then give it its rightful place in my ever-growing number of bookshelves and boxes. It’s not unusual for me to read several books at the same time. This drives my wife crazy in her efforts to keep our house neat and orderly. So I’ve long hoped for the day when I could have books that take up no space and yet are instantly accessible whenever the mood struck to read one of them. In short, I needed a practical electronic book reader.

E-book readers are not a new idea, but like many nascent technologies, they appeared on the scene well in advance of cost effective technology or even a convenient way to purchase content that would have allowed them to compete favorably with traditional books. In the past year, Amazon.com launched what is arguably the first mass-marketed e-book reader called the Kindle. The Kindle appears to have achieved a level of success that had eluded previous e-book reader products, including several competent designs from well established companies like Sony.

A few essential features for an e-book reader are ease-of-use, portability, and long battery life. Thanks to the introduction of high resolution e-ink displays, which draw very little power, a new generation of e-book readers has emerged that has allowed the e-book a better chance to gain market acceptance.

Another important e-book feature that had been lacking previously was the ease of content acquisition. Amazon has done a great job in this area thanks to their significant offering of more than 140,000 e-book titles in addition to many popular magazines and newspaper subscriptions. But the biggest breakthrough for Kindle, in comparison to its competitors, has been the content acquisition and delivery method. Amazon decided to take on the considerable challenge of installing a cellular modem in each Kindle. The logistics of this undertaking are significant. By partnering with Sprint, Amazon can get wireless data coverage over most of the U.S. which alleviates the need for a customer to install any software on a PC or even physically connect the device to a PC to periodically load content on to the Kindle (although it is still an option). The books and magazines can be purchased directly from and delivered to the Kindle, lending considerable temptation for customers to buy books on impulse. Kindle owners are even able to download significant samples of books that include a ‘buy it now’ button at the end of the sample thus eliminating much of the friction of an e-book acquisition. After all, who wants to stop reading a book after you’ve already read the first 20 pages and can’t wait to see what happens next?

I’ve downloaded books previously and attempted to read them on my laptop or PC but I found it difficult. Part of the problem was that I wanted to take the book with me, from room to room, or with me when I traveled. That’s not easy to do with a laptop computer because it’s awkward and heavy to carry around a notebook computer for reading. It also takes a while to boot, and with each program I install on the laptop, the boot process slows down even more. Secondly, the battery life on my notebook is only 100 minutes, hardly enough time to make it a convenient reading device. All rechargable batteries lose capacity as they age. And it costs about $120 for a new battery pack. So, like many others, I tend to live with this continually decreasing battery life rather than replace the battery every year. But the biggest downside of reading something like a downloaded book on a laptop has been that there was no easy way to keep my place in the book. Each time I rebooted the computer, I needed to re-find my place in the book. That’s just not acceptable. Granted, things are getting better with software e-readers, but the other disadvantages of laptop computers as e-book readers are just too hard to overcome.

E-book readers have done a lot to get around these problems. The Kindle will last for several days of reading on a charged battery that is 1/10 the size of a typical laptop battery (6 Wh vs 60 Wh). And when the battery loses its capacity over its life, Amazon offers a replacement battery for $20. I can change the battery myself, something that I can’t do very easily with my iPod. Instead, Apple recommends I return their products to a service center at considerable inconvenience and significant expense to replace the battery. So I congratulate Amazon for making the Kindle battery easy to replace and offering it at a reasonable price.

After using the Kindle nearly every day for a few weeks, I like it more and more, particularly the ease of acquiring new books at a reduced cost over conventional books. Best of all, these e-books take up no space around the house. The only downside is that I can’t borrow or lend the Kindle books like I can with a physical book. And sharing the Kindle with Terri is not easy since only one person can use it at a time. Amazon allows up to 5 Kindles on a single account that would all have access to my growing e-book library, but that would be expensive. I guess that’s the downside of digital media, it’s so easy to copy that if they don’t protect it by locking it to each customer, then no one will pay for it. In some ways, that’s more fair to the author too, since a book that gets passed around means that there is less compensation for the author per book. But unlike physical books, you can get free books that are out of of copyright. There are about 20,000 books, including many classics, available for free on feedbooks.com in a ‘mobi’ format which is compatible with Kindle.

I couldn’t wait to tell Peter about my Kindle because I thought he’d be interested in a ‘green’ reading device which will save a few trees. Also, it consumes so little energy that I can recharge it with a small solar panel. But instead, he seemed somewhat suspicious of the newfangled gadget and asked me how it ‘felt’ and how it ‘smelled’ indicating that these are important sensory experiences when it comes to reading books. Terri is equally suspicious and cannot imagine replacing her paperbacks with this gadget. She’s agreed to run an experiment by reading a book of her choosing on it. However, her patience for new technology is limited and for her to be pleased with it, it would have to be superior in every way to a paper book, so I’m not holding out much hope that she’ll become an e-book convert.

I generally don’t buy the first generation of a new technology product. In fact, I had planned to wait for Amazon to offer a second generation Kindle prior to getting one, figuring that it would have many improvements over the first genera
tion. But after learning that the Kindle design would not be refreshed this year, I decided to get one. It also helped by getting an offer for a $100 discount through a credit card promotion Amazon offered, so I got one for $259. I see they are back up to $359. If I continue at the rate I’ve been buying books, Amazon should make a good profit from me. I’ve already read 6 books in 3 weeks, 2 free ones and 4 that I purchased from Amazon. I also converted several large 100+ page industry reports to a Kindle-compatible format and read them on a plane trip to California. So I’ve really been getting a lot of use out of it.

I think that the e-book reader market shows great potential and after a few false starts it just may be poised to catch on and allow people do their daily reading without killing as many trees in the process.

National Renewable Energy Lab visit

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A few weeks ago I visited the National Renewable Energy Lab open house in Golden, CO with a few other members of the Northern Colorado Clean Energy Network. I’d wanted to see this facility for some time, and figured that an open house on a Saturday would allow some of our members who normally are unable to attend our energy tours during the week to join us. As it turned out, we only had 4 members of our group show up. Despite the low turnout, we had a good time carpooling there and back because we got to chat for a few hours about renewable energy topics.

The NREL has a visitor’s center and there was a presentation in progress when we arrived about how to do an energy audit on one’s home. Several of us had just been to an NCRES presentation on this topic recently so we did not sit down to listen to the presentation. The presentation took up much of the visitor’s center display area, making it impossible to talk without disrupting the presentation so our ability to wander around inside was a bit limited.

The exhibits were very nicely constructed and a docent explained the various renewable energy programs underway and the purpose of the various buildings on the campus. There are numerous projects going on all over the facility, but unfortunately they are off-limits for visitors. Only the visitor’s center is accessible. I had expected this to be the case, and so I tried to gather some information about what would be necessary to get a tour of the actual laboratories in the hope that some future visit would allow us to get better access to what’s going on in the labs. I can see that it will be a challenge as they are not set up to handle tours of the actual labs.

The docent who was our guide had spent most of his career in the power field, and I had a long discussion with him about transmission of power over high voltage DC lines. Transmitting power over DC lines is counter-intuitive for most engineers who were taught that you can only transmit utility scale power on AC lines. But thanks to advances in high power semiconductor components to handle utility scale power, DC power transmission lines are becoming more common to deliver electrical power long distances and to help isolate grids through interties. This method of transmitting power will become more important in the future as some of the best potential sources of renewable power generation such as wind and solar tend to be far removed from population centers. HVDC power transmission has the advantage of being able to isolate the grids so that the need to control the phase of the AC power over long distances is not required. The largest DC line in the U.S. is the Pacific DC Intertie which takes hydroelectric power from the Columbia River in Washington State and delivers it to customers in the Los Angeles area.

My favorite Visitor’s Center exhibit was the section of the GE 37-meter wind turbine blade. I’ve seen these blades up close during our Ponnequin Wind Farm tour, but was curious about the materials of construction. With the section exposed, I saw that the materials looked identical to those used in my LongEZ and Cozy. They consisted of wood, foam, fiberglass, and epoxy albeit on a much larger scale that what is used in my planes.

Me and Ed Miccio standing next to the GE blade section

You can see that the spar and caps are very thick on these blades.


The Cozy uses the same materials and construction techniques as the wind turbine blades.

The NREL visitor’s center is open from 9-5 Monday through Friday and I’d highly recommend that if you ever find yourself in the vicinity of I-70 at exit 263, you should stop by for a short visit and self-guided tour.

Midnight Engineer’s Forum

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Each year I attend a conference in Denver that grew out of a magazine called ‘Midnight Engineering‘. The magazine was dedicated to engineers that loved the work so much they could be found doing it at all hours, even in their spare time, hence the magazine’s name. Many of the readers were entrepreneurial types engaged in moonlighting activities. A yearly conference called Entcon was started that became like a ‘real-time version of the magazine’. It was a great networking event with lots of interesting people that kicked off with skiing in the Rocky Mountains followed by a weekend of presentations and informal networking sessions.

The magazine is out of print, but a conference which is now called Entconnect is still going on each year in Denver around the last week of March.

We don’t get a chance to talk much with the other conference participants throughout the year, so I’ve put together a forum on Yahoo Groups. If discussions about entrepreneurship, tech startups, and free agent engineering appeal to you, perhaps you’d like to join the group.