Podcast about Solar Thermal
Renewable Energy World did an in depth podcast on the solar thermal earlier this year that I just listened to last week. It’s a good listen for anyone interested in solar energy technoloogy to heat their domestic hot water, what types of technology are out there, and some important things to consider before selecting a solar thermal system.
Listen to the Podcast: Realizing the Potential of Solar Thermal
BACnet: A Tutorial Overview
A new link on the EnergyAnalysis links page to “BACnet – A Tutorial Overview” sumarizes the genesis of BACnet and how it works.
This tutorial is housed on the official BACnet website with a growing list of tutorials at http://www.bacnet.org/Tutorial/index.html, including:
- “BACnet – A Tutorial Overview”
- “BACnet/IP”
- “Understanding BACnet Encoding”
- BACnet – Der neue Standard für die Gebäudeautomation
Google and Utilities Partner on Smart Metering Technology
Eight utilities in the U.S., Canada and India are teaming up with Google in smart meter projects that will enable customers to monitor their energy use online and better manage their power consumption.
NPR – Smart Meter Saves Big Bucks for Pa. Family
Low E technology & double-glazed windows…
Low E (Emissivity) technology uses microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor (explained below) by suppressing radiative heat flow. A typical low E coating is transparent to the solar spectrum (visible light and short-wave infrared radiation) and reflective of longwave infrared radiation.
The National Fenestration Rating Council (NFRC) label, which appears on all window, door, and skylight products rated by Energy Star, summarizes a window’s performance in terms several factors listed below.
Reading the NFRC Certified Window Label
U-value (U-factor) is a measure of the rate of non-solar heat loss or gain through a material or assembly. It is expressed in units of Btu/hr-sq ft-ºF (W/sq m-ºC), where sq ft (sq m) represents per square foot (square meter) of window area and ºF (ºC) represents per degree temperature difference between indoor and outdoor temperatures. Values are normally given for NFRC/ASHRAE winter conditions of 0ºF (18º C) outdoor temperature, 70º F (21º C) indoor temperature, 15 mph wind and no solar load. The U-factor may be expressed for the glass alone or the entire window, which includes the effect of the frame and the spacer materials. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value.
Solar Heat Gain Coefficient (SHGC) measures the fraction of incident solar radiation admitted through a window (both directly transmitted and absorbed) and subsequently released inward.
Visible Transmittance (VT) measures how much visible light is transmitted on a scale from 0 and 1.
Air Leakage (AL) measures the rate at which air passes through cracks in the window, in terms of cubic feet of air per minute per square foot of window area (cfm/ft^2). Most industry standards and building codes require an AL of 0.3 cfm/ft^2.
In most cases the U-factor, which is found in the top left box on the NFRC label, is the most important number to consider when evaluating windows for thermal insulation and energy efficiency.
Double-Glazed Windows
The figure on the left illustrates the characteristics of a double-glazed window with high solar gain and low E glass. The term “double glazed” means two layers of glass separated by a spacer and sealed at the edges. You can find different types of low E windows with either high solar gain or low solar gain. High solar gain is best suited for buildings located in heating-dominated climates that experience cold winters. High solar gain admits heat from the sun, while a low U-factor due to the low emissivity prevents the escape of heat. This type of window is good for passive solar design relative to other types of windows with low E coating and low solar gain. A double-glazed window with low solar gain and low E glass is suitable for cooling-dominated climates and hot summers.
Related Links
Efficient Windows Collaborative: Window Selection Tool
Efficient Windows Collaborative: Window Operating Types
National Fenestration Rating Council: The NFRC Label
National Fenestration Rating Council: The Facts About Windows & Heat Loss
PG&E: Energy Efficient Window Glazing Systems for Commercial Facilities
NPR: Energy-Saving Windows A Legacy Of ’70s Oil Crisis
Alside: Glossary of Window Industry Terms
Kansas State Energy Extension Service: Building Envelope: WIndows and Doors
How Energy Is Used in Commercial Buildings
The US Energy Information Administration (EIA) conducts the Commercial Buildings Energy Consumption Survey (CBECS) every four years. The CBECS looks at the energy consumed by different types of commercial buildings in the United States. EIA will release the 2007 CBECS in mid-2009. Here’s an overview (Figure 1 & 2) of the 2003 CBECS, which was based on a sample size of 5,215 buildings, representative of a total population of 4.9 million commercial buildings and 71.6 billion square feet of floor space in the U.S.
Figure 1. Electricity accounts for more than half of energy consumed by commercial buildings.
Figure 2. More than half of energy consumed in commercial buildings is used for space heating and lighting.
Lies, Damn Lies, and… Henry Gifford critical of LEED study
Henry Gifford, a maverick NYC mechanical systems designer, has written a highly critical objection to the first broad study done by the US Green Building Coucil (USGBC). The study intended to determine how much energy LEED rated buildings actually used.
USGBC commissioned the New Buildings Institute (NBI) of Vancouver, Washington, to conduct the study, Energy Performance of LEED for New Construction Buildings, which claimed that “On average, LEED buildings are 25-30% more efficient than non-LEED buildings.”
Gifford has presented a different analysis, critical of the USGBC / NBI study. Gifford suggests that in reality the LEED rated buildings are, on average, 29% less efficient than average U.S. buildings. If you haven’t seen Gifford’s presentation, it’s worth a watch (youtube clip below). The full critique, “A Better Way to Rate Green Buildings“, is also available on his website, along with the US Green Building Council’s response to Gifford’s criticique in an e-mail that USGBC sent to its chapter leaders, and Gifford’s rebuttal to the USGBC response.
Gifford points out a few flaws in the study…
California: First State to Mandate Disclosure of Energy Use at Time of Building Transaction
California is the first state to mandate disclosure of commercial buildings’ energy use to prospective buyers, lessees, or lenders, and it is requiring building owners to use the EPA ENERGY STAR online tool, Portfolio Manager, to get the job done. A new California law, Assembly Bill 1103, requires all commercial building owners or operators to disclose their buildings’ benchmarking data and Portfolio Manager performance rating to prospective buyers, lessees of entire buildings, or lenders starting in 2010. The state also has broken new ground by requiring all state-owned buildings to be benchmarked with Portfolio Manager.
BuildingGreen.com – Regulations Demanding Actual Data Are Leapfrogging LEED
Smart appliances and dynamic demand in the US and the UK
In the the first quarter of 2009, General Electric will introduce a suite of ”smart” appliances or energy management enabled appliances that will receive a signal from the local utility and react based on the appliance’s internal programming. GE needs utility companies to collaborate in this endeavor. There are over 3,000 utilities in the US. GE is currently conducting a pilot program in Louisville, KY in partnership with Louisville Gas and Electric Company (LG&E).
A similar pilot program in the UK will evaluate smart fridges. The electric and gas utility npower, is working with the RLtec to trial a dynamic demand program that substitutes load response for generation station response, balances supply and demand, improves the thermal efficiency of the electric grid, facilitates renewable generation integration, and mitigates system faults, all with no discernable impact on load performance. In the first phase of the UK program, 300 fridges fitted with RLtec’s technology will be distributed to npower consumers. Eventually the trial program will deploy 3,000 fridges and freezers of different types and models and assess the benefits of the technolgy.
Manhattan’s Geothermal Potential
NEW YORK TIMES – For millions of years, invisible streams of water have run deep in the earth below Manhattan at a constant temperature of 65 degrees, a source of energy that seems beyond exhaustion — and beyond reach. But eight months ago, a seminary in Chelsea began to pump water from those streams to heat its buildings in the winter and cool them in the summer.
College Sustainability Report Card: Green Buildings
College Sustainability Report Card provides in-depth sustainability profiles for hundreds of colleges in all 50 U.S. States and Canada. See the results. There are several categories of sustainability used in their report card. The Green Building category 51 schools earned “A” grades in the green building category, which looks at schools’ adoption and use of high-performance green building design. Most of them have numerous LEED certified buildings on campus. The average grade for the green building category was “C+.”
Click on the green building leaders listed below to view report cards.
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EIA: Retail Prices
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