Energy Efficiency of Power Production: How Supercritical Carbon Dioxide Turbines Operate

Duane M. Tilden, P.Eng.                                    Sept 1, 2018

Foreword:

This is another article in an ongoing series of reports on the technological development of supercritical carbon dioxide in the power production and energy efficiency sectors of industry, power plants and utilities.

dodge-sco23 supercritical CO2 turbine

Figure 1. Size comparison of Supercritical Power Turbine to Conventional Steam Turbine (1)

Abstract:

The ever increasing search for improving energy and power production efficiency is a natural quest as developments in technology seek to be utilized to improve operations and supply cost effectively. The technologies behind the utilization of supercritical carbon dioxide and other such fluids have long been established. We are furthering our exploration into this sector of power production developing new technologies along the way to a smarter economy and modernization of infrastructure.

The Principle of Operation

Supercritical fluids can play an important role in developing better electricity generators because of their liquid- and gas-like properties. A supercritical fluid is an optimal working fluid because it has a temperature and pressure above its critical point, meaning that it doesn’t have a definite liquid or gas phase. Consequently, the slightest changes in pressure or temperature cause huge changes in the material’s density.

With any supercritical fluid, the ease of compressibility goes up, explains Stapp, so it becomes something more like water. Because supercritical CO2 also compresses more easily than steam, the amount of work done during the compression phase—normally accounting for 25 percent of the work performed inside the system—is dramatically reduced; the energy saved there greatly contributes to the turbine’s overall efficiency.

“We expand it like a gas, and pressurize it like a liquid,” says James Pasch, principle investigator of the Supercritical Carbon Dioxide Brayton Cycle Research and Development Program. “You can do this with any fluid, but supercritical carbon dioxide matches really well with ambient temperatures.”

Carbon dioxide is optimal for this application because it doesn’t go through a phase change at any point during the cycle. Its critical temperature, 88 degrees Fahrenheit, is very close to ambient temperature, which means the heat emitted by the turbine is the same temperature as the surrounding environment. Supercritical carbon dioxide is also very dense; at its critical point, the fluid is about half the density of water. So, in addition to being easier to compress, less work is required to cycle it back to the heat source for re-expansion.

The Brayton Cycle also offers direct environmental benefits. For one, it’s carbon neutral. The system takes carbon dioxide out of the air and puts it in the recompression cycle loop. Just as important is the fact that the system limits water usage by minimizing discharge, evaporation, and withdraw.

“That’s a big deal for the southwest,” says Gary Rochau, manager of Sandia’s Advanced Nuclear Concepts Department. Sandia’s generator can work in places where water is in limited supply. This puts it on par with the Palo Verde Nuclear Power Generating Station, a nuclear power plant in Arizona that uses recycled waste water as cooling water, saving groundwater and municipal water supplies for other uses. (2)

Figure 1. Illustration of a Supercritical CO2 Turbine [Peregrine Turbine Technologies] (2)

Advances in Materials and Technology

GE Reports first wrote about Hofer last year when he 3D printed a plastic prototype of the turbine. His team, partnered with Southwest Research Institute and Gas Technology Institute, has since submitted the design to the U.S. Department of Energy and won an $80 million award to build the 10 MW turbine. The turbine features a rotor that is 4.5 feet long, 7 inches in diameter, and only weighs 150 pounds. The engineers are now completing a scaled-down, 1 MW version of the machine and will test it in July at the Southwest Research Institute.

The idea of using CO2 to power a steam turbine has been around for a while. It first appeared in the late 1960s, and an MIT doctoral student resurrected it in 2004. “The industry has been really interested in the potential benefits of using CO2 in place of steam in advanced supercritical power plants,” Hofer says.

By “supercritical” Hofer means efficient power stations using CO2 squeezed and heated so much that it becomes a supercritical fluid, which behaves like a gas and a liquid at the same time. The world’s most efficient thermal power plant, RDK 8 in Germany, uses an “ultrasupercritical” steam turbine operating at 600 degrees Celsius and pressure of 4,000 pounds per square inch, more than what’s exerted when a bullet strikes a solid object.

Hofer says that the steam power plant technology “has been on a continuous march” to increase efficiency and steam temperature, but once it tops 700 degrees Celsius, “the CO2 cycle becomes more efficient than the steam cycle.” Hofer’s turbine and casing are made from a nickel-based superalloy because it can handle temperatures as high as 715 degrees Celsius and pressures approaching 3,600 pounds per square inch. “You need a high-strength material for a design like this,” he says.

 Figure 2. GE Global Research engineer Doug Hofer is building a compact and highly efficient turbine that fits on a conference table but can generate 10 megawatts (MW), enough to power 10,000 U.S. homes. The turbine, made from a nickel-based superalloy that can handle temperatures up to 715 degrees Celsius and pressures approaching 3,600 pounds per square inch, replaces steam with ultrahot and superpressurized carbon dioxide, allowing for a smaller design.

The hellish heat and pressure turn CO2 into a hot, dense liquid, allowing Hofer to shrink the turbine’s size and potentially increase its efficiency a few percentage points above where state-of-the-art steam systems operate today. “The pressure and fluid density at the exit of our turbine is two orders of magnitude higher than in a steam turbine,” Hofer says. “Therefore, to push the same mass through, you can have a much smaller turbine because the flow at the exit end is much denser.”

Hofer’s design uses a small amount of CO2 in a closed loop. “It’s important to remember that this is not a CO2 capture or sequestration technology,” he says. Hofer says that the technology, which is being developed as part of GE’s Ecomagination program, could one day start replacing steam turbines. “It’s on the multigenerational roadmap for steam-powered systems,” he says.

By virtue of becoming more efficient, the technology could help power-plant operators reduce greenhouse gas emissions. “The efficiency of converting coal into electricity matters: more efficient power plants use less fuel and emit less climate-damaging carbon dioxide,” wrote the authors of the International Energy Agency report on measuring coal plant performance. (3)

Previous Blog Posts on Supercritical Carbon Dioxide:

  1. https://duanetilden.com/2016/11/11/transitioning-oil-gas-wells-to-renewable-geothermal-energy/
  2. https://duanetilden.com/2016/03/13/supercritical-co2-used-for-solar-battery-power-system/
  3. https://duanetilden.com/2015/04/23/doe-invests-in-super-critical-carbon-dioxide-turbine-research-to-replace-steam-for-electric-power-generators/
  4. https://duanetilden.com/2013/10/29/supercritical-co2-refines-cogeneration-for-industry/
  5. https://duanetilden.com/2013/10/29/supercritical-co2-turbine-for-power-production-waste-heat-energy-recovery/
  6. https://duanetilden.com/2013/10/29/waste-heat-recovery-using-supercritical-co2-turbines-to-create-electrical-power/

 

References:

  1. supercritical-carbon-dioxide-power-cycles-starting-to-hit-the-market/
  2. supercritical-carbon-dioxide-can-make-electric-turbines-greener
  3. ecomagination-ge-building-co2-powered-turbine-generates-10-megawatts-fits-table/
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Microgrids and the Blockchain – Transforming the Energy Supply

Author: Duane M. Tilden, P.Eng.           Date: June 10, 2018

In the transition from the centralized utility is the development of the Micro-grid.  The Micro-grid offers many benefits to society, including; (a) use of renewable energy sources that reduce or eliminate the production of GHG’s, (b) increases in energy efficiency of energy transmission due to shortening of transmission distances and infrastructure, (c) improved municipal resilience against disaster and power reductions, and finally, (d) promotion of economic activity that improves universal standard of living. (1)

The Brooklyn Microgrid Experiment

A Network of Energy Cells (2)

In order to be successful, blockchain platforms and microgrids require a regulatory framework. In New York State, such a framework is provided by “Reforming the Energy Vision” (REV). The platform’s objectives are to minimize the vulnerability of the power supply system that became visible during Hurricane Sandy, to use more sources of renewable energy, and to reduce costs.

The Brooklyn Microgrid is a good test case for these objectives. “A microgrid is a nucleus that sets the stage for an energy future consisting of networks of energy cells,” says Stefan Jessenberger from Siemens’ Energy Management Division. “Blockchain also supports this process, because it makes it much easier to conduct energy trading within cells.”

Siemens Digital Grid, next47, and LO3 Energy all believe in the potential of blockchain-based microgrids, because this technology can be used wherever there are decentralized energy sources. “Our experiences with the Brooklyn Microgrid will certainly flow into future projects,” says Kessler.

 
Image #1: A Canal in Brooklyn, New York (5)

The Future is Now

But something else is happening to the grid as energy generation changes – the rise of microgrids. These smaller grid systems are linked to localised power sources, often referred to as “distributed generation” sources. For example, a handful of buildings in a city with their own solar panels might be connected to nearby residences.

In fact, that is exactly the model that LO3 Energy has experimented with in its Brooklyn Microgrid project. Customers signed up to it can choose to power their homes via a range of local renewable energy sources. People with their own solar panels can sell surplus electricity to their neighbours, for example. It’s a peer-to-peer network for electricity.

To ensure that accurate records of these transactions are kept, LO3 has opted to use blockchain distributed ledger technology. This means the microgrid’s accounting is decentralised and shared by everyone on the network.

“It’s virtually unhackable,” says founder and chief executive Lawrence Orsini, explaining that tampering with these records is almost impossible because of the fact that everyone has their own, regularly updated copy of the ledger.

LO3 is now rapidly expanding with a series of other projects around the world. One is based in South Australia, where Orsini explains there is already a lot of distributed generation going on – and plenty of grid stability issues. Users can now experiment with LO3 to get access to electricity from solar-fuelled batteries nearby when needed. (3)

Physical and Virtual Microgrids

Challenging the traditional electrical supply model are microgrids. The “microgrid” term normally refers to a localised grid that can disconnect from the main grid and operate autonomously. It uses local sources of energy to serve local users, integrating the supply of energy from various producers, including local power generators and providers of renewable energy such as solar power. Consumers with their own energy production capabilities (wind turbines or solar energy systems) can sell their surplus energy production back to peers in the microgrid, on a pay-per-use basis (becoming ‘prosumers’).

While physical microgrids are still rare, we do observe the development of virtual microgrids using peer-to-peer energy trading. Blockchain is just one element in the transformation of electricity supply, providing Distributed Ledger Technology (DLT) to members of a peer-to-peer energy network, or microgrid. It offers [or ‘provides’] a reliable, lower-cost digital platform for making, validating, recording and settling energy transactions in real time across a localised and decentralised energy system.

With increasing demand for more flexible energy supplies we expect a continued increase in the number of virtual microgrids and a gradual movement towards true, physical microgrids along 4 stages […] (4)

“This project…, is the first version of a new kind of energy market, operated by consumers, which will change the way we generate and consume electricity.”
New Scientist (5)

References:  

  1. microgrid-as-a-service-maas-and-the-blockchain/
  2. smart-grids-and-energy-storage-microgrid-in-brooklyn
  3. http://www.wired.co.uk/article/microgrids-wired-energy
  4. energy-and-resources/articles/will-microgrids-transform-the-marke.html
  5. http://brooklynmicrogrid.com/

Renewable Energy and Heat Pumps – Net Zero Energy by Design

As a mechanical engineer I spent 17 years in design of mechanical systems. Always seeking the best solution given budgets and adhering to efficient design principles. Often we can combine systems by hybridization, where two technologies come together in a synergistic match. I have used hybrid technologies, using ground loops and air-air fluid coolers, with heat pumps successfully in the mechanical design and construction of a number of buildings.

While wind energy may be harvested, it is not always available. Some regions get more wind than others, and there may be governmental or civic restrictions. For renewable energy, solar may be a better option than wind, even though it is only available during the day. In either case some form of auxiliary power will be required, such as batteries,  grid connection, fuel powered generator, or hydro-power.

The use of heat pumps allows for the provision of a number of heating and cooling devices which may be connected to a central circulating building loop. As heat pumps have operating temperatures generally between 40F to 90F, although it may vary depending on heat energy source, such as air, water or ground.  Air temperatures may vary during the day and season. As air temperature drops, heat pumps lose efficiency. We can see this in the following figure. (1)

air-source-heat-pumps-cold-weather

In the case of geothermal heat pump system design, there are some options. One method is to run a water source such as a pond, river, body of water in an open loop design,  in a closed loop method using an process waste heat stream or ground coupled system. Either system is usually connected to a heat-exchanger to which is connected a second closed house loop. The house loop is controlled to either discharge or gain heat from the geothermal loop.

I am attaching  a blog post (2) from 2007 where I made a comment in 2009. This blog post is still getting comments. I believe such systems can be designed and constructed and would contribute to a “Net-Zero” building systems.

I am a lawyer who has been interested in the subject of energy conservation since the seventies. Back when we had the first OPEC crisis, I thought this country would head in a direction away from the consumption of huge quantities of oil and gas. It didn’t happen. Now of course, our thirst for oil has been the primary reason for a preemptive war with no end in sight. Moreover, peak oil seems to be here. And so far nothing much seems to have changed. But the public, may at last be ready for something different.

There are some real promising things happening with new solar energy systems and with wind turbines. It is long past due. But I still keep wondering whether we are approaching this problem of solving our energy demands the right way. With both solar and wind systems all technology seems to be headed toward the creation of electricity. Electricity is definitely useful but often inefficient.

Heating and cooling costs are about 60-70 percent of home energy costs. It is far more cost effective to use heat transfer than to make heat. Water source heat pumps are 300-400 percent efficient while the best ordinary HVAC systems might be forty percent efficient. (Are they that much?) What if you could even vastly surpass the efficiency of a water source heat pump. How? By making the wind pump the water instead of an electric pump.

Why not use wind to its best advantage? Make the wind do what it has done very efficiently for hundreds of years: pump water. Make it pump water from a warm place to a cold place and make it store the heat where the heat is needed or wanted. In the winter pump the heat from under the ground into the house. In the summer pump the heat from house into the ground.

To do this, because of the wind’s variability, one would need a huge (?) thermal sink in the house to slowly release the heat transferred from underground to the heat sink or to transfer the heat from the house to the ground while the wind was not blowing.

A four part system. A wind turbine. A pump. A closed loop of pipe. An interior thermal sink.

It is fairly well known that in most climates, five or six feet below ground, the temperature is a about 55 degrees. I think it is quite possible to take advantage of the geothermal underground temperature by using a wind turbine to pump water from underground into an interior thermal sink. If a large enough volume of water could be circulated to where the interior heat sink reached 55 degrees, I think such a home’s heating and cooling costs would be drastically reduced.

If the large thermal sink could get the house temperature substantially raised in the winter and substantially cooled in the summer, very little additional energy might be required to bring it to a desirable temperature with the use of a water source heat pump. A water source heat pump would work in tandem very well by using the internal heat sink as a convenient source to operate a water source heat pump.

My idea would be to use a vertical wind turbine on the roof coupled to an Archimedes screw to pumps and circulates water through the closed loop. The vertical wind turbines seem to need less wind, have more torque, and are quieter. I also think that from an architectural point of view, they would look much more attractive, especially the ones that look like spinnerets. They also take advantage of a sloping roof which increases wind speed.

I also think the Archimedes screw would be an ideal pump. It requires no gears or lubrication and could attach by a straight shaft to the vertical wind turbine. An Archimedes screw would be very inexpensive as pumping systems go and extremely reliable as there is really nothing to break.

I have other ideas about roof design and about turbine design for greater efficiency. I also have ideas about the plumbing. What I would like to see is whether there are people out there who think this idea has commercial merit and if so, how we might go about making wind driven water pumping for geothermal transfer a success. We would need some engineering and architectural expertise and some ability to fabricate the wind turbines and pumps.

I look forward to responses.

Duane Tilden said…

I have been looking at the latest responses and it seems to me there is some confusion about this idea.

Firstly, heat pump technology, as pointed out achieves it’s high COP’s from the phase change. It is through the leveraging of the refrigerant phase change from a fluid to the gas phase where heat energy can be obtained from low temperature heat sources. This is how geothermal heat pumps can obtain heat energy from relatively low temp sources such as the ground where nominal ambient water temp would be at 55F and deliver hot water at temps of 90F to 140F.

Alternatively heat pumps can be used in air/air, air/water, water/air and water/water configurations. These are generally stand alone devices where in a properly engineered installation do not require supplemental heat sources.

Wind energy is a separate sustainable, environmentally friendly application. In my opinion the OP’s idea of using wind energy to move water around for a heat pump application is marginal and likely too capital intensive to realize any real benefit. Also, it is just too restrictive, in my opinion.

Wind energy converted directly to electricity, or other dedicated pumping applications where electricity is not available is best (water pumping up to a reservoir in agricultural or power generation schemes for example). There also may be some merit to the idea of storing the energy as compressed air, but the amount of heat generated would not be significant, usable heat source. Try heating your home with a candle.

Electricity is used by a wide range of applications, so why not use the wind energy to best effectiveness? The operation of the compressor in the heat pump and the pumps to run the water loop(s) require electricity, so do common home appliances.

There may be some applications where the proffered idea would make sense, but not likely widely applicable for single family residences unless you have a large property and money to burn.

SEPTEMBER 26, 2009 AT 10:44 PM

 

References:

  1. heat-pump-effective-temperature-range/
  2. wind-turbine-heat-pump-geothermal

The BC Energy Step Code – Missing the Point

The BC Energy Step Code is currently being implemented in British Columbia as an answer to future energy considerations in new building construction. It achieves this claim of moving towards “Net Zero” building construction by utilizing a building envelope first approach with modeling and a performance test.

The idea is that by raising a building’s theoretical energy efficiency a building will become a net zero home. In the process, there is a requirement for a certified and licensed energy adviser to be involved in the modeling, construction and testing phases of the building. (1)

In conjunction with this approach is the claim that builders can construct these buildings being “fuel-neutral”. Using this rationale the roles of mechanical systems design, testing and commissioning are omitted in the performance considerations of the building.

However, a net-zero building must include the omitted systems as the design and operation of necessary systems. These may include the ventilation and exhaust systems, water heating, laundry, and heating systems. Also, rain-water collection for irrigation and gray water systems or other load reduction schemes may all may contribute to the energy consumption and success of a “net zero” building.

Some of these services will always be required in a municipal setting such as electrical, water and waste. Reduction strategies are advised as further increases in population will add additional loads at existing consumption rates which might overload existing supply and waste systems infrastructure such as pipes and cable.

The final answer to how a building performs will be in the overall utility bills paid by the building for its operation. This includes the electrical power, gas consumption, solid and liquid waste disposal and water supplied. Unless you live in a remote rural area where none of these services are provided by a municipality, there will always be a design component of the mechanical systems that contributes to the operation of an energy efficient home.

References:

  1. How the BC Energy Step Code Works

 

Turning to Net Zero for Buildings – The HERS Index

Over the last few months my time has been occupied with travel and work. Relocation and working in construction has consumed certain amounts of time. In the process I have continued to learn and observe my working environment from the perspective of a mechanical engineer.

I have upgraded some of my technology, investing in a smart phone for it’s utility and ease of connection. However, this newer tech is still not the best for longer term research and curation efforts, such as this blog. I am happy to report I have managed to land a longer term residence which now will provide me the needed stability and access to resources, while I can set up my work space needed for more intensive endeavours.

Now relocated in Vancouver, I have a few projects in the works, and am able to get back to focusing some of my time into my own research and development, to which, is one of the major purposes of my blogging. Next week, on September 25th there is a luncheon course presentation I plan on attending regarding upcoming changes to the BC Building Code introducing The Energy Step Code. More on this topic later after the seminar.

In California we already see the movement on towards the construction of net zero buildings, as compliance to the 2016 Building Energy Standard which applies to “new construction of, and additions and alterations to, residential and nonresidential buildings.” (1) These rules came into effect January 1st, 2017. I will be reviewing this publicly available document and provide more insight and commentary at a later time.

One measure of rating homes for energy efficiency that I have seen often referenced and may be a tool for reporting and rating homes is the HERS Index as shown in the graphic.

Image 1:  HERS Index scale of residential home energy consumption.

As we can see from the scale that there is reference home, so there are calculation needed to rate a home, computer methods are available online where a houses data can be input for a curious homeowner, however qualified ratings are to be done by a qualified HERS Rating technician. These ensure by performance tests that a house meets standards in actual use and perform as claimed.

A comprehensive
HERS home energy rating

The HERS Rater will do a comprehensive HERS home energy rating on your home to assess its energy performance. The energy rating will consist of a series of diagnostic tests using specialized equipment, such as a blower door test, duct leakage tester, combustion analyzer and infrared cameras. These tests will determine:

  • The amount and location of air leaks in the building envelope
  • The amount of leakage from HVAC distribution ducts
  • The effectiveness of insulation inside walls and ceilings
  • Any existing or potential combustion safety issues

Other variables that are taken into account include:

  • Floors over unconditioned spaces (like garages or cellars)
  • Attics, foundations and crawlspaces
  • Windows and doors, vents and ductwork
  • Water heating system and thermostats

Once the tests have been completed, a computerized simulation analysis utilizing RESNET Accredited Rating Software will be used to calculate a rating score on the HERS Index. (3)

As buildings become more expensive and are asked to provide ever more services there will be a movement to make these building more efficient to operate and maintain. As we do more with less, there will be social impacts and repercussions. To some these changes may be disruptive, while enabling newer markets in energy efficiency, renewables, energy storage, micro-grids and net zero buildings, to name a few.

References:

  1. California Building Code Title 24 – 2016 Building Energy Efficiency Standards for Residential and Nonresidential Buildings.
  2. Understanding the HERS Index
  3. How to Get a HERS® Index Score

High Efficiency Clothes Washers

Nowadays we are searching for more ways to be energy efficient at home, work and elsewhere.  Our resources are not infinite, even if they are renewable. And, as such, we should be seeking ways to reduce our energy and water consumption, not only to be a good citizen but also for the money it saves which can be utilized elsewhere.

Yesterday I did my laundry, packed all my smelly and soiled clothes in a plastic garbage and headed off to the laundromat in Canmore. I chose a double loader which cost $4 + another buck for the heavy soiled clothing option. Not sure how this thing worked, I bought two small boxes (it’s a double loader after all so two boxes should do, I thought) of Tide for a buck apiece.
Samsung WF210ANW High Efficiency Washer

Figure 1.  Image of a Samsung’s WF210 HE Washing Machine top loading washing machine. (1)

The instructions on the machine were not clear, so I opened the boxes and sprinkled them on my clothes, set the temp for warm and started the machine. It was a 30 min cycle, and after about 5 minutes I did not see any appreciable amount of water in the washer, also I noticed that there was a slot for the detergent. So, I decided to buy another box of detergent and put it into the pull out. The machine was on 10 minutes now, and still no water… wtf?

Image result for high efficiency washing machine

Figure 2.  Graphic comparing a HE washing machine to a traditional top loader. (2)

Okay, so I call the management which operated the local motel, informing them that the machine is broken, and a girl comes out to see what is going on. She assures me it’s fine and working, that the machine uses very little water. Okay, I am skeptical and concerned that with so much detergent and very little water my clothes would not get clean and be covered with a residue.

In the meantime a nice German lady comes over to me and says that she has never seen a top loader before and they only use front loading machines where she is from. I laughed and told her that in Canada we have a tendency to waste our resources as we have so much, whereas in Germany they have a larger population crammed in a small country. The government of Canada has a tendency to give lip service to energy and water efficiency.

The end result was that the clothes came out brilliantly clean with no residue. Most of the water was spun out and the clothes were only slightly damp, which meant that my dryer time was greatly reduced. The amount of heated water and energy used for drying is greatly reduced. Is it not time to get rid of the energy hogs?

 

References:

(1)  High Efficiency Washing Machines Save Money With Less Water, Energy

(2)  High Efficiency Washing Machine

Water Conservation and a Change in Climate Ends California Drought

Water scarcity is becoming a greater problem in our world as human demands for water increases due to population growth, industry, agriculture, and energy production. When the water supply is being pushed beyond its natural limits disaster may occur.  For California residents the end of the drought is good news.  Return of wet weather raises reservoir levels and effectively prevents wildfires.  However, another drought could be around the corner in years to come.  Thus government and water users need to remain vigilant and continue to seek ways to conserve and reduce water use.
ca-reservoirs 2017 End of drought.png
Figure 1. 2017 California Major Water Reservoir Levels
By Bark Gomez and Yasemin Saplakoglu, Bay Area News Group (1)
Friday, April 07, 2017 05:17PM

Gov. Jerry Brown declared an end to California’s historic drought Friday, lifting emergency orders that had forced residents to stop running sprinklers as often and encouraged them to rip out thirsty lawns during the state’s driest four-year period on record.

The drought strained native fish that migrate up rivers and forced farmers in the nation’s leading agricultural state to rely heavily on groundwater, with some tearing out orchards. It also dried up wells, forcing hundreds of families in rural areas to drink bottled water and bathe from buckets.

Brown declared the drought emergency in 2014, and officials later ordered mandatory conservation for the first time in state history. Regulators last year relaxed the rules after a rainfall was close to normal.

But monster storms this winter erased nearly all signs of drought, blanketing the Sierra Nevada with deep snow, California’s key water source, and boosting reservoirs.

“This drought emergency is over, but the next drought could be around the corner,” Brown said in a statement. “Conservation must remain a way of life.” (2)

References:

  1. https://wattsupwiththat.com/2017/04/08/what-permanent-drought-california-governor-officially-declares-end-to-drought-emergency/ 
  2. http://abc7news.com/weather/governor-ends-drought-state-of-emergency-in-most-of-ca/1846410/

What Does Moist Enthalpy Tell Us?

“In terms of assessing trends in globally-averaged surface air temperature as a metric to diagnose the radiative equilibrium of the Earth, the neglect of using moist enthalpy, therefore, necessarily produces an inaccurate metric, since the water vapor content of the surface air will generally have different temporal variability and trends than the air temperature.”

Climate Science: Roger Pielke Sr.

In our blog of July 11, we introduced the concept of moist enthalpy (see also Pielke, R.A. Sr., C. Davey, and J. Morgan, 2004: Assessing “global warming” with surface heat content. Eos, 85, No. 21, 210-211. ). This is an important climate change metric, since it illustrates why surface air temperature alone is inadequate to monitor trends of surface heating and cooling. Heat is measured in units of Joules. Degrees Celsius is an incomplete metric of heat.

Surface air moist enthalpy does capture the proper measure of heat. It is defined as CpT + Lq where Cp is the heat capacity of air at constant pressure, T is air temperature, L is the latent heat of phase change of water vapor, and q is the specific humidity of air. T is what we measure with a thermometer, while q is derived by measuring the wet bulb temperature (or, alternatively, dewpoint…

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California adopts nation’s first energy-efficiency rules for computers

The California Energy Commission has passed energy-efficiency standards for computers and monitors in an effort to reduce power costs, becoming the first state in the nation to adopt such rules. Th…

Source: California adopts nation’s first energy-efficiency rules for computers

Benchmarking Buildings by Energy Use Intensity (EUI)

There are many metrics and measurements when it comes to evaluating energy as we use it in our daily lives.  In order to compare between different sources or end uses we often have to make conversions in our terms so that our comparisons are equitable.  This may be further complicated as different countries often use different standards of measure, however, we will convert to common units.

Benchmarking

Benchmarking is the practice of comparing the measured performance of a device, process, facility, or organization to itself, its peers, or established norms, with the goal of informing and motivating performance improvement. When applied to building energy use, benchmarking serves as a mechanism to measure energy performance of a single building over time, relative to other similar buildings, or to modeled simulations of a reference building built to a specific standard (such as an energy code). (1)

Benchmarking is a common practice in buildings to establish existing consumption rates and to identify areas that require improvement and to help prioritize improvement projects.  These benchmarks can be established for a building, system within a building, or even a larger campus, facility or power source.  Usually an energy or facility manager will determine energy consumption over a fixed period of time, 1 to 3 years, and compare it to similar facilities.  Normalized by gross square footage of the building the EUI is usually expressed as kBtu/sf per year.

Energy Intensity (EI) of a Country

Figure 1:  Energy Intensity of different economies The graph shows the amount of energy it takes to produce a US $ of GNP for selected countries. (2)

Not to be confused with Energy Use Intensity, Energy Intensity is an economic measure of energy use normalized by the GDP of a country and is considered a measure of a Nation’s Energy Efficiency.  Countries with a high EI have a higher cost to convert energy into GDP, whereas countries with low EI have lower costs of converting energy into GDP.  Many factors contribute to the EI value, including climate, energy sources and  economic productivity. (2)

Energy Use Intensity (EUI)

The EUI of a building includes the electrical power use and heating fuel consumption for heating and hot water generation.  Many facilities require different loads according to their primary use or function, including cooling and refrigeration.  For the comfort of occupants electricity is needed for lighting and plug loads to meet the functioning needs of the equipment in the facility.  Heating, ventilation and air conditioning (HVAC) may require electricity or another fuel such as natural gas.  Hot water may be generated with electricity or a fuel.  A site may also have solar PV or hot water, wind power, and daylighting programs.  There are also many strategies which may be employed by building operators to reduce loads and energy consumption including controls, storage, micro-grid, purchasing offsets, etc.

When comparing buildings, people not only talk about total energy demands, but also talk about “energy use intensity” (EUI).  Energy intensiveness is simply energy demand per unit area of the building’s floorplan, usually in square meters or square feet. This allows you to compare the energy demand of buildings that are different sizes, so you can see which performs better.

EUI is a particularly useful metric for setting energy use benchmarks and goals. The EUI usually varies quite a bit based on the building program, the climate, and the building size. (3)

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Figure 2.  Typical EUI for selected buildings.  This graph is based on research EPA conducted on more than 100,000 buildings (4)

Site Energy vs Source Energy

As we go forward into the future, it is rather unclear how current events will affect the international agreements on reducing carbon consumption.  However, generally speaking, renewable energy sources are seen to becoming more economic for power production.  For many facilities this means that supplementing existing grid sources for power with on-site power production is making economic sense.  Future building improvements may include sub-systems, batteries and energy storage schemes, renewable sources or automated or advanced control systems to reduce reliance on grid sourced power.

The energy intensity values in the tables above only consider the amount of electricity and fuel that are used on-site (“secondary” or “site” energy). They do not consider the fuel consumed to generate that heat or electricity. Many building codes and some tabulations of EUI attempt to capture the total impact of delivering energy to a building by defining the term  “primary” or “source” energy which includes the fuel used to generate power on-site or at a power plant far away.

When measuring energy used to provide thermal or visual comfort, site energy is the most useful measurement. But when measuring total energy usage to determine environmental impacts, the source energy is the more accurate measurement.

Sometimes low on-site energy use actually causes more energy use upstream.  For example, 2 kWh of natural gas burned on-site for heat might seem worse than 1 kWh of electricity used on-site to provide the same heating with a heat pump.  However, 1 kWh of site electricity from the average US electrical grid is equal to 3.3 kWh of source energy, because of inefficiencies in power plants that burn fuel for electricity, and because of small losses in transmission lines.  So in fact the 2 kWh of natural gas burned on site is better for heating. The table below provides the conversion factors assumed by the US Environmental Protection Agency for converting between site and source energy. (3)

References:

(1) BUILDING ENERGY USE BENCHMARKING  https://energy.gov/eere/slsc/building-energy-use-benchmarking

(2) ENERGY INTENSITY  https://en.wikipedia.org/wiki/Energy_intensity

(3) MEASURING BUILDING ENERGY USE  https://sustainabilityworkshop.autodesk.com/buildings/measuring-building-energy-use

(4) WHAT IS ENERGY USE INTENSITY (EUI)?  https://www.energystar.gov/buildings/facility-owners-and-managers/existing-buildings/use-portfolio-manager/understand-metrics/what-energy