Nate Adams asked whether the heat pump was modulating its electric use to maintain temperature or cycling on and off? The power data (below) show it is cycling on and off.
The graphs below are for the last 30 hours or so and overlap with some of the data I posted yesterday. They also include another night of heating with the 18 kBtu/h heat pump. The first graph is what Home Assistant gets from the Mitsubishi Kumo Cloud interface regarding the settings of the heat pump. The second graph is the Govee temperature data and the third is electric power from both the heat pump (blue) and the electric heaters (purple).
For most of this time I am heating with the heat pump. In early afternoon (2-4PM) solar gain through the windows causes the Govee temperature to rise above set point and the heat pump throttles back. The HP was turned off from 4-8AM yesterday to heat for 2 hours with electric then 2 hours with propane. The electric heater power data are shown in purple.
The first graph clearly shows that the set point (purple) is 63F while the measured temperature of the wireless sensor (blue) bounces between 64 and 65. I simply do not understand why the Mitsubishi control software maintains an average temperature above the set point.
As I have indicated, this heating season I will be using my guest house in Maine to study the energy performance of two Mitsubishi mini-split heat pumps. Already some interesting results are emerging. So far this season, with outside temperatures 23°F and above, the heat pumps demonstrate considerable energy (and cost) savings as compared with electric, baseboard heat. My students and I are starting to quantify the savings. Here I report on some preliminary results.
We have three ways to heat the guest house: 1) Two Mitsubishi mini-split heat pumps (one 6kBtu/h and the other 18kBtu/h), 2) A 20,000 Btu/h Rinnai propane vented wall furnace, and 3) three 1.5 kW ceramic electric heaters (together, 15,400 Btu/h) distributed throughout the open space. Each of these three systems has its own remote thermostat. The heat pumps each have a wireless remote thermostat mounted on the wall across the room. The Rinnai is controlled remotely by an Emerson Sensi thermostat, also wall-mounted across the room. And the three ceramic electric heaters are individually plugged into smart outlets that are controlled by Home Assistant using software to mimic a simple on/off thermostat, with temperature measured by a Govee WiFi thermometer sitting on a cabinet near the Sensi thermostat. Because the Govee thermometer reads in 0.1°F increments, it is the common metric used for determining the Cottage inside temperature.
My Home Assistant Heating Dashboard is shown below. All of the heating and monitoring systems can be remotely accessed.
Solar gain is a big factor during the day, so our heating experiments are conducted at night. Last night we heated the guest house for several hours using three of the four heating systems (just used one heat pump). The results are shown below. The first graph shows the Govee temperature from 4 PM yesterday through 10 AM this morning (11/14). Until 4 AM space temperature was maintained by the 18 kBtu/h heat pump. Early yesterday the set point for the heat pump was 65°F but was lowered to 63°F around 6:40 PM yesterday. At 4 AM the heat pump was turned off and the interior temperature was maintained for the next two hours with the three 1.5 kW electric heaters. At 6 AM heat switched from electric to propane. Both the propane and electric heat had set temperatures of 64°F. At 8 AM the propane heat was terminated and control was given back to the 18 kBtu/h heat pump.
The outside temperature, measured with our Ambient weather station is graphed below. The purple lines indicate when the heating system was changed. From midnight on the outside temperature stayed within 2°F of an average value of about 31°F.
The electric power to the heat pump and the electric heaters were continuously monitored. The average electric power to the heat pump between midnight and 4 AM was 553 Watts. From 4AM to 6AM the electric heaters had an average power of 1830 Watts. That is, the electric heaters used 3.3X the power used by the heat pump. Without adjusting for the change in outside temperature this implies a heating COP = 3.3. This is great news. It means 3.3X lower heating cost than with electric resistive baseboard heat.
But there seems to be a small price to pay for this energy savings. The temperature regulation with the heat pump is not nearly as good as with either of the other two heating systems. The heat pump caused temperature swings of about 2°F while the other two systems have swings of only 1/5th this amount. Moreover, the average temperature maintained by the heat pump is well above its 63°F set point. (Even when you graph the temperature determined by the heat pump’s remote wireless sensor you see that it is always above the set point.) One has to wonder why the control software for the heat pump is not able to do a better job of maintaining the desired temperature. There appears to be no ability to change the “deadband.” for this unit.
We are still working on metering the propane flow in order to understand the energy use for the propane heater. We hope to have this metered soon, it has proven more difficult than we imagined.
But even without metering the propane, I know how much propane should have been burned from 6 – 8AM. From 4-6 AM the electric heaters provided 1.830kW x 2 h = 3.7 kWh of heat. I am paying $0.30/kWh for electric so my cost for this electric is $1.10. 3.7 kWh of energy is equivalent to 12,500 Btu. My propane furnace is rated at 80% efficiency. So to deliver this amount of heat requires that it burn 15,600 Btu of propane. The energy content of a gallon of propane is 91,452 Btu. So I would have had to burn 0.171 gal of propane which, at a cost of $4.29 per gallon, would cost me $0.73.
Hence, 2 hours of heat last night cost me $1.10 using electric heat, $0.73 using propane, and $110/3.3 = $0.33 using the electric heat pump, this with an outside temperature of nearly freezing. The only downside of the heat pump is the lack of temperature control. I am optimistic, however, that we can learn how to use the heat pump better to achieve better control.
One final thing to note is that when I look at the specs for this Mitsubishi compressor, MUZ-FS18N it appears to me that for a wet-bulb outside temperature of about 30°F and a dry-bulb inside temperature of 65°F the heating COP should be 3.21, consistent with my measurement of 3.3.
A few weeks ago in my post I described how one of my four Mitsubishi mini-split heat pumps was using excessive energy. Today’s post provides additional information about that. Apparently the excessive energy is by design! For background please revisit my August 12 post.
Just a quick recap — In the last three years I have had four, low-temperature, mini-split heat pumps installed on my property in Maine. The oldest of these is a 15 kBtu/h unit that is installed in my house living room. The model number for its outdoor unit is MUZ-FH15NA. The other three units were installed over the next two years. Their outdoor units have model numbers: MUZ-FS06NA, MUZ-FS18NA, and MUZ-FS06NA. (Apparently the “FS” models are improved over the “FH” models.) All four compressors use R410A refrigerant.
These units have seen minimal use since the beginning of May. On rare occasions we have used them for a bit of cooling or heating. They have simply remained in standby mode for nearly 120 days. Three of these use 3-4 W of continuous standby power but the oldest, the 15 kBtu/h unit, particularly during the night, experiences 70W power spikes every two hours or so that last for about 10 minutes. This causes this unit to use about 0.2 kWh per day more energy than the other three. For three months I have been seeking to understand what is going on.
Back in June I emailed my installer, Dave’s Appliance, questions about this performance including graphs and other details. I have always found Dave’s to be extremely helpful. They could not explain what was going on so they passed the information along to their Mitsubishi support team. A couple of months went by with no answer.
I pestered them some more. Finally, in mid-August, two technicians from Dave’s drove the 50 miles from Winthrop to my house to make measurements on the compressor while on the phone with their Portland Mitsubishi tech support. With the travel time, these guys spent a half day addressing my issue. The only measurements they made were to confirm that a certain thermistor had the correct value.
One of the techs who came to my house was Ean Laflin, the heat pump service manager with Dave’s Appliance. After he was done troubleshooting and speaking with Mitsubishi he explained that there was a 70 W heater in the compressor, and that the control board turned it on whenever the ambient temperature was below 68F. Presumably after the heater ran for 10 minutes the temperature of the thermistor rose above the set point causing the heater to turn off. (It is my impression that there is oil in this compressor, and this heater is intended to keep the viscosity of this oil low so the compressor will start easily when called upon.)
But this begs the question, why would this heater be activated when the ambient temperature ranges from 60F to 68F? I could see the need to heat the oil during the winter. But in my part of Maine from May – October the ambient temperature is usually above 68F for much of the day and usually drops below 68F late at night. For nearly four months I have not needed this heat pump yet the heater keeps using energy, night after night. The only way I can avoid this is to shut off the circuit breaker. This is obsurd!
So why doesn’t this same thing happen with my other three heat pumps? Ean tells me that the control board on these slightly newer models is shipped with a jumper that can be set so as to disable this feature — apparently this is the default setting. He can change the jumpers on the other three heat pumps so that all four of my heat pumps run this heater and waste energy. But there is no jumper to change on my Living Room heat pump to reduce its standby power to 3W like the other three heat pumps.
I conclude from this that Mitsubishi, after shipping thousands or perhaps millions of heat pumps with this control strategy determined it was not necessary and “improved” the next generation of control boards. The only way to “improve” my heat pump would be to install a new control board. I recognize this is not a cost effective way to save the $15/year wasted by this heater.
Which leads me to my last point. Each one of my four heat pumps is connected to the internet and can be controlled using the Kumo Cloud App. Why can’t Mitsubishi download updated firmware over the internet to fix this bug? Hundreds of millions of devices (phones, etc.) that only cost a few hundred dollars can receive updated firmware over the internet. Why can’t Mitsubishi figure this out for heat pumps that cost many thousands of dollars? The technology really needs to be updated.
The town of Oberlin, OH was essentially built on a swamp. Oberlin basements commonly experience water problems. When we first purchased our Oberlin home in 1988 there were a few storm events that left water puddles in our basement. Various measures eliminated this problem, but high summer humidity remains an issue. For years we have employed a basement dehumidifier to prevent mold and mildew.
Our house in Maine also has humidity issues. We are on the Atlantic coast where the relative humidity is always above 70%. Both our house and guest cottage are built on granite ledge sloping down to the water. I wouldn’t have thought so, but it turns out the granite ledge is relatively porous to water flow. After every rain storm, water flowing down the hill towards the river creates water issues in our crawl spaces. Dehumidifiers have proved to be important to prevent condensation on our water pipes and mildew on the wood.
I have read that you need to keep the relative humidity level in your crawl space below 60% to prevent problems. The usual way to accomplish this is to 1) prevent water from entering the crawl space using water and vapor barriers, and 2) use a dehumidifier to remove what water does enter.
I have three dehumidifiers located in 1) our guest cottage crawl space, 2) house basement/crawl space, and 3) our Oberlin house basement. All three are plugged into smart plugs that record their energy use. The two Maine units are commercial units from AlorAirand the Oberlin one is a Honeywell residential unit.
In Oberlin I have a heated basement, so the dehumidifier never has to remove water from cold air. The Honeywell unit can handle that. I do not run it during the winter. In contrast, the Maine crawl spaces are not heated and get quite cold. The AlorAir commercial dehumidifiers can remove water even when the air temperature is in the 40’s. I ran both of them last winter — not sure if I need to and will try to figure that out.
The graph below shows they day-to-day energy use of our guest cottage. As the graph shows, the dehumidifier uses 4-5 kWh of energy daily.
The AlorAir unit uses 600 W when the compressor is running. I normally leave its set point at 60% relative humidity and the compressor cycles on and off. A typical graph of its power vs time is shown below.
When I lower the set point the duty cycle increases (i.e., time that the compressor is on is longer) and the daily energy increases — all as expected.
I am a bit worried about the frequent cycling of the above dehumidifier. I don’t understand why the control doesn’t include a larger “deadband” so that the compressor does not switch on and off so frequently. I attempted to reach out to AlorAir to learn more but I found their technical support to be unresponsive.
The first graph above shows that the dehumidifier used much more energy on July 17. The reason for this is that I decided to try cooling the guest cottage air by circulating it through the crawl space. This exposed a continuous source of humid, warm air to the dehumidifier and it ran nearly continuously. After one day I concluded this was not the optimum way to cool the cottage.
The average energy used by the dehumidifier in my Maine house for July has been 3.4 kWh/day. The area of the house crawl space is larger than that of the cottage, but it is better sealed. Unlike the cottage the crawl space floor in the house is fully sealed with concrete.
The average energy used by the dehumidifier in in Oberlin for July is about 12 kWh per day. Our house there is over 100 years old and all the walls lack modern vapor barriers. The graph below shows the power used by this dehumidifier. This unit removes about 60 pints of water daily and runs almost all the time during the summer.
This dehumidifier is about a year old. My experience with these “basement units” is that they work well for a few years. After a few years they continue to use lots of energy but don’t remove much water. When I bought this Honeywell unit last fall, the dehumidifier it replaced was 4 years old. I ran the two of them side by side for a few days and found the new unit removed water at a rate 5X that of the old one (even though they had the similar specs and were using similar energy). It is hard to throw the old one away because it still removes water — just not good at it.
What I don’t know is the importance of keeping the relative humidity of my Maine crawl spaces low in the winter. My instinct is to believe that mildew and mold won’t grow during the winter in my cold crawl spaces even if the relative humidity is high. But when the temperature warms in the spring I need to keep the humidity level below 60%. But this is just a hypothesis. So far I am erring on the side of caution and running the dehumidifiers year round. They just use less energy in the winter.
I would like to reduce the energy and carbon emission associated with dehumidification. That would be accomplished by raising the relative humidity set point on the dehumidifier. But under no circumstances can I tolerate mold or mildew. I would be interested in learning what people have to say about this issue for cold and warm weather. Is RH% a relevant metric when the air temperature is low as is the case in the winter? Does it make sense to use lots of energy to achieve 60% relative humidity in a crawl space whose temperature is below 45F? I don’t know the answer to these questions and would value informed input.
I figure it would be too boring for me to post detail after detail about my Home Assistant (HA) automation system implemented in Maine. Instead I will share some things we have learned using the system, and along the way provide some details relevant to the particular post.
Today’s post is to share energy-use data I have gathered on three generations of refrigerators, purchased in 1985, 2006, and 2022.
As mentioned in my last post, 2 years ago we began construction of a guest house at our property in Maine. Last summer we began using the guest house and installed in it a new, LG 20 cubic foot refrigerator with ice maker. We bought the refrigerator from our local Home Depot.
We purchased our Maine property in 2000. The property included a 3-bedroom ranch-style house and a saltwater dock. On the dock was a small 12′ x 24′ fish house. Both structures had refrigerators. In 2006 we purchased a new, Admiral refrigerator for the main house. The refrigerator in the fish house was a GE model, presumably new in 1985.
So, this summer I find myself using three refrigerators, one (LG in the cottage) purchased in 2022, a second (Admiral in the house) purchased in 2006, and the third (GE in the fish house), presumably purchased in 1985. Being a scientist, I just couldn’t resist measuring and comparing their daily electric use.
My HA instance records data from a variety of smart sensors. A device I have found particularly useful and reliable is the Sonoff S31 smart plug which costs about $10. These outlets communicate via WiFi and allow one to use a phone app to turn them on and off, and also provide real-time data on the electric power being used. They are also compatible with Home Assistant.
Being especially nerdy I decided to re-configure the plugs by installing Tasmota firmware on them. I purchased an inexpensive device to accomplish this with a laptop and usb port. My Oberlin colleague and friend Bill Mohler made me a jig to connect this to the ESP8266 boards (inside the S31 smart plugs) without soldering wires. About a month ago I installed the Tasmota firmware on 12 of these devices. (I watched several YouTube videos to figure out this process.) Each of my three refrigerators were plugged into their own S31/Tasmota smart plugs and I recorded their daily electric use with HA.
The results, while not unexpected, are rather dramatic . They are shown in the graph below.
Before June 13 the oldest refrigerator used about 4 kWh/day while the newest refrigerator used 0.73 kWh/day. We currently pay about $0.25/kWh for electricity in Maine. The difference in energy costs for the two refrigerators is $0.81/day. This corresponds to $300/year in excess electric costs (for a 365-day year) for the oldest fridge — as compared with the newest!
With literally 1 week of monitoring it was clear that we needed to replace the dock fridge with a newer one. (Mind you, I have been using this refrigerator for 23 summers.) On June 13, for a cost of $680, Home Depot delivered a 20-cu ft LG fridge and hauled away the old GE fridge. The energy savings is obvious.
We actually use the dock fridge only 5 months of the year, so the annual payback is (5/12)*$300 = or $123/year. The simple payback time is 5.5 years.
And, of course, there are other positive returns. The old GE fridge had broken shelves and did not look so nice. The newer LG model is cleaner and nicer.
Then there is the carbon savings. EPA’s e-grid says that the carbon content for Maine’s region of the electric grid (NEWE) is 0.54 lbs CO2/kWh. The annual savings (based on 5 mos use) of 500 kWh represents an annual reduction of 270 lbs of CO2 emission. The savings would be greater in many regions of the country where the carbon footprint of the grid is larger.
And yes, I should have replaced the house refrigerator (used year round) with the new LG, and moved the Admiral to the fish house. The prospect of emptying the fridge and moving it was just too much that day. Maybe next summer I will find the energy to do that.
Bottom line — this upgrade is a no-brainer. My $680 investment in a new refrigerator has a higher rate of return than anything in my retirement portfolio or bank accounts.
Of course, this is not news. Numerous organizations like Efficiency Maine are working diligently to promote efficiency upgrades.
25 years ago David Goldstein of the NRDC came to speak to my Oberlin College class on Energy Science and Technology to tell us how voluntary efficiency standards negotiated with appliance manufacturers had steadily produced more and more efficient appliances. This trend is captured in a graph published in the 2008 APS Efficiency study report of which David Goldstein was a coauthor.
So, I have not made a new discovery. Still, it is useful to be reminded that a little investment now can yield tremendous savings when it comes to energy efficiency.
I think it has been two years since I have posted on this blog. This post is the beginning of a new direction for me.
A couple of years ago my wife and I built a small guest cottage on our property in Maine. Mostly we will use this in the summers, but we decided to go ahead and make it a year-round house. I also decided to make it a laboratory for understanding the performance of a couple of heat pump technologies.
The house is outfitted both with a Rinnai direct vent propane furnace as well as two Mitsubishi, low-temperature, mini-spit heat pumps. We were going to use an electric hot water heater but, instead, decided to install a Rheem hybrid heat-pump hot water heater. Heat pump hot water heaters offer the potential for considerable energy savings in the summer, but savings in the winter are less obvious. I am anxious to study this.
For the next year I intend to report on my findings for this guest cotttage. I have some systematic experiments planned to answer questions such as:
what is the efficiency (or heating COP) for these heat pumps at different outside temperatures
how does the cost of heating with propane compare to those using electric heat pumps
how does the carbon footprint compare between propane and heat pumps
do night time setbacks produce energy savings with heat pumps as they do with propane
how does the energy use of my heat pump hot water heater compare with an electric hot water heater
what is the impact of the heat pump hot water heater on my winter heating costs
I hope to yield definitive answers to some of the above questions. No doubt other questions will come up along the way.
I am primarily interested in the winter performance of these systems.
During the summer we will have guests using the cottage and that will make it difficult to control various parameters. During the winter my wife will be using the cottage during the day as her office. In the evenings it will be unoccupied — which leaves me excellent opportunity to control the environment. Both day and night the indoor temperature will be closely controlled and documented.
To record data and to control parameters we are running Home Assistant (HA) on a Rasberry Pi 4. All of the relevant devices in the cottage communicate with HA. This allows me to both read and control the heat pumps, hot water heater, propane heater, various temperature and humidity sensors, lights, dehumidifier, electric heaters, etc. Iammeter energy monitors have been installed on the main electric panel and both heat pumps. These communicate with HA, as well. There is also a weather station about 100 ft away from the cottage connected to Weather Underground.
Our main house also contains two Mitsubishi mini-split heat pumps. These, too, along with iammeter power meters attached to each, are monitored with HA.
While a lot of the instrumentation was being developed and installed this last year, we do have some preliminary results worth sharing. These will be the subject of upcoming posts.
Our study is based on public municipal building energy benchmarking data from 10 US cities for the year 2016. The entire dataset contains annual energy use and energy-related greenhouse gas emission for over 28,000 properties, of which about 4500 are classified as office. By cross-referencing the benchmarking data with the USGBC LEED Project Database we were able to identify 551 office buildings that were certified in LEED systems that address whole building energy use. These systems were LEED for New Construction (NC), Core & Shell (CS), and Existing Buildings (EB). We have compared the 2016 site energy, source energy, electric energy, non-electric energy and greenhouse gas (GHG) emission of these LEED-certified offices other offices in the same cities in order to understand energy savings associated with LEED certification.
In this post I will talk about the site energy savings observed for LEED offices.
LEED offices in every city were found to use less energy on-site than non-LEED offices, adjusting for size, of course. Except for Washington DC, however, the variability in LEED performance was so large that these savings were not statistically-significant at the usual, 95% confidence level. In aggregate, however, the savings were statistically significant. The results are shown in the figure below.
The red symbols indicate savings in site EUI by LEED office buildings relative to other office buildings in the same city. The error bars represent the 1-sigma standard errors in these savings. In aggregate (ALL CITIES) and in Washington DC the savings are two standard deviations or more above zero. In other cities the savings have larger error. In aggregate the LEED site energy savings is 8.5 kBtu/sf, which represents an 11% savings relative to the site EUI for non-LEED offices. These results are consistent with those we have reported earlier based on 2015 data for Chicago.
It should be noted that these savings are substantially lower than the 30-35% energy savings frequently asserted for LEED buildings – but are nonetheless positive and significant.
I will discuss savings in other metrics in upcoming posts.
On March 14, 2019 the US Green Building Council (USGBC) finally awarded the Hotel at Oberlin its LEED-platinum rating after earning 81 points under the LEED NC v2009 system, just over the 80-point minimum required for the platinum rating. This milestone comes as a relief to Oberlin College which has for three years falsely claimed the Hotel at Oberlin to be a LEED-platinum building. But a good day for Oberlin College is a bad day for the US Green Building Council because there is nothing exemplary about the Hotel’s energy performance — it is the very definition of mediocrity. This latest member of the elite club of LEED-platinum hotels – I think it is the fifth such hotel in the U.S. – uses more energy per square foot than do 75% of other U.S. hotels and uses more natural gas than any other Oberlin College building except its Science Center.
The design team for the Hotel at Oberlin projected that it would annually use 1.43 million kWh of electric energy and 8,350 therms of natural gas. These energy projections, if realized, would correspond to a site EUI of 56 kBtu/sf and a source EUI of 151 kBtu/sf. The LEED Scorecard for the building shows that the USGBC awarded the building the maximum possible points for energy efficiency –19 out of 19 possible.
Had the Hotel achieved this projected target energy, however, it would not be an impressive accomplishment. This target site EUI is still higher than that of 25% of the estimated 30,000 U.S. Hotels We know about energy use by U.S. Hotels from the 2012 Commercial Building Energy Consumption Survey (CBECS). The graph below shows the SiteEUI distribution for U.S. Hotels as determined from this survey. It is clear that the projected site EUI use for the Hotel at Oberlin is lower than 75% of these hotels. A similar statement can be made about the projected source EUI for the hotel.
More importantly, the Hotel at Oberlin has never achieved this projected energy use figure. Since opening nearly three years ago the natural gas use has been 4-6 times higher than projected by its design team! For the last 12 months the electric and natural gas use have been 1,680,000 kWh and 48,000 therms, respectively. These correspond to annual site and source EUI of 104 and 215 kBtu/sf, respectively. The graph below shows that this SiteEUI for the Hotel at Oberlin is higher than that of 75% or 22,500 of U.S. Hotels. The energy performance of this LEED Platinum Hotel is worse than mediocre.
The bottom line is that the Hotel at Oberlin, one of only five LEED-platinum hotels in the US, has energy use that is typical of U.S. Hotels — near the middle of the distribution. There is nothing noteworthy or remarkable about its energy use, either site or source. Its certification as one of the nation’s most energy-efficient hotels is simply an embarrassment to the USGBC. It illustrates how meaningless energy efficiency points are for LEED certification.
Late last year a group from Harvard’s T. H. Chan School of Public Health published a paper entitled, “Energy savings, emission reductions, and health co-benefits of the green building movement” in Nature’s Journal of Exposure Science & Environmental Epidemiology. In their paper MacNaughton, Cao, Buonocore, Cedeno-Laurent, Spengler, Bernstein, and Allen consider the cumulative energy savings of some 20,000 commercial buildings, world-wide, that have been certified under the U. S. Green Building Counci’s Leadership in Energy and Environmental Design (LEED) since the program’s inception. Their focus is to calculate environmental co-benefits associated with this (assumed) energy savings. Unfortunately their entire thesis is predicated on assumptions that are not supported by facts. Their paper, masquerading as a peer-reviewed journal article, is little more than a marketing brochure for the USGBC and is devoid of credibility.
MacNaughton et al. make the naive assumption that LEED-certified buildings demonstrate, year after year, the energy savings their design teams predicted during the certification process. This was essentially the same assumption that underpinned the now-discredited Kats report from 2003. Numerous studies have shown that buildings in general, and green buildings in particular, use significantly more energy than predicted by their design teams. This so-called “building performance energy gap” is pervasive and well-documented. The Harvard paper is entirely based on the results of the 2008 NBI study which has long been discredited.
Frankly these energy-performance assumptions are sophomoric. The authors cite only three references to support their assumptions — all published a decade ago — and they misrepresent the results of one of these papers — I know, because I wrote it! They apparently are unaware of upwards of 12 studies published in the last decade that look at energy performance of LEED buildings.
The Harvard paper should have been rejected in the review process. If I were at liberty to do so I would publish the reviews of my critique as they affirm essentially all the claims I have made. One of the Harvard authors served on the Board of the USGBC which should have raised a red flag. The paper was received by the Journal on October 12, 2017 and accepted for publication five days later. This accelerated time frame raises questions about the substance of the peer-review process. And finally, the authors make several factual claims about LEED buildings in their paper that are simply incorrect.
As more and more building energy data become available a consistent picture is emerging that shows that LEED-certified buildings use no less primary energy than other buildings. The latest contribution in this area is a paper soon to be published in Energy and Buildings entitled, “Energy Performance of LEED-Certified Buildings from 2015 Chicago Benchmarking Data.” This paper compares the annual energy use and green house gas emission for some 130 LEED-certified commercial buildings in Chicago with that of other Chicago buildings in 2015. Chicago, it turns out, has one of the highest rates of LEED-certification among major U.S. cities.
The data clearly show that the source energy used by LEED-certified offices, K-12 Schools, and multifamily housing is no less than that used by other similar Chicago buildings. In the case of K-12 Schools, LEED-certified schools actually use 17% more source energy than other schools!
Many studies that address building energy use only discuss energy used on site, called site energy. We found that LEED-certified buildings in Chicago use about 10% less energy on site than do other similar buildings. No doubt green building advocates will emphasize this apparent energy savings.
But energy used on site – called site energy – is only part of the story. Site energy fails to account for the off-site losses incurred in producing the energy and delivering it to the building – particularly important for electric energy that, on average, is generated and distributed with 33% efficiency. The EPA defines source energy to account for both on- and off-site energy consumption associated with a building; building Energy Star scores are based on source energy consumption. The issue is similar to one encountered when comparing the environmental impact of electric vehicles with internal combustion vehicles — you must trace the energy back to the electric power sector.
How is it that LEED buildings use less energy on-site than other buildings while consuming more source energy? Simple — more of their (indirect) energy use occurs off-site in the electric power sector. They use less natural gas but more electric energy than other buildings. Essentially a larger fraction of their energy use occurs off-site in the electric power sector.
This is the trend in newer buildings, to use more electric energy and less natural gas or district heat energy. Part of this is convenience and part of it is driven by the belief, or rather hope, that the electric power sector will soon be dominated by renewable energy. It is true that the contribution of renewable energy (solar, wind, etc.) in the electric power sector is growing, but this is a very slow process and, for many years to come, natural gas and even coal will remain the dominant source for electricity.
This trend is not unique to LEED buildings — it is present in all new buildings. When you compare Chicago’s LEED buildings with other Chicago buildings of similar vintage you find that they use similar site and source energy.
Bottom line, 2015 Chicago data show that LEED-certified buildings are not providing any significant reduction in energy use or GHG emission.
The Pragmatic Steward 