Green Roof Resource

Yesterday the House Subcommittee on Energy and Air Quality (part of the Committee on Energy and Commerce) held a hearing focusing on building energy efficiency as one method of tackling CO2 emissions. The subcommittee is presently developing and understanding various potential mechanisms to reduce greenhouse gas emissions by 60-80% by 2050 in a manner that limits costs to the economy and maximizes the efficiency of a mandatory climate change program. They have produced a white paper that analyzes cap-and-trade program options. While developing cap-and-trade programs will most likely focus on large-scale stationary sources and transportation, yesterday’s hearing demonstrated that members of Congress recognize and are exploring the significant reductions that can occur through improving the energy efficiency of our buildings. Wahoowa!

One of the facts that was mentioned multiple times during the hearing is that building stock represents 40% of total US greenhouse gas emissions. To reduce emissions by 60-80% by 2050, improvements in building efficiency must be made. The committee recognizes that sizable reductions can be made through improved building energy efficiency. Last year the committee and the House passed a new building code to states to advance energy efficiency, but the legislation was stopped by Senate action. The witnesses spoke of several different programs and efforts to formulate a national building energy efficiency policy. The challenge appears to be to create incentives to further energy efficiency without setting standards that are unachievable or of limited use depending upon the location of a building project.

Here are a few of programs and efforts that were mentioned in the hearing:
The 30% solution: The Energy Efficient Codes Coalition has launched a campaign to improve residential energy efficiency standards by 30% from the 2006 international energy code standards. In September, this will be decided at the International Code Council Annual Conference in Minneapolis, Minnesota. The 30% solution is designed to be achievable, affordable, and enforceable. This is the most promising effort for enforceable change in building construction at the moment, but we’ll see where this stands in two months time.

“Beyond code”: This was another often used phrase yesterday. This refers to voluntary program such as EnergyStar. I’ve mentioned EnergyStar before, but another source for energy efficiency ideas is EnergySavers, which provides energy information and tips from DOE, EPA, and HUD.

With representatives talking about efficiency targets and executive agencies and departments collaborating, change is certainly coming. Who knew that “state of the shelf” technologies could be so exciting?

The WEF Sustainability Conference was held this week in Washington, DC. During the conference, a multitude of available resources were recommended to learn more about green infrastructure and sustainable water management. Below is a brief list of the resources in no particular order that I found interesting. I’ve included links where appropriate. I’m still trying to track down a book that was mentioned during the opening session, Sustainable Watershed Management. Any additional information on it would be helpful.

1. The Santa Clara Valley Water District has taken significant efforts to reduce energy and water consumption through water conservation and recycling programs. Their efforts are summarized in a 2007 report entitled
From Watts to Water.

2. With climate change affecting the frequency and magnitude of storm events, JP Morgan has recently published a guide to evaluating corporate risk with a focus on water. The report, Watching Water, provides tools for assessing impacts on companies due to decreased water quantity and quality.

3. The Civil Engineering Environmental Quality Assessment and Award Scheme (CEEQUAL) is an awards scheme for acknowledging excellent environmental quality on civil projects. CEEQUAL was developed in the UK and is based upon a points system.

4. The Pacific Institute has developed two water to air models. These models provide information on the energy and air quality effects of water management projects in urban and agricultural water districts.

While San Francisco has had a green building map (developed by M. Landman Communications & Consulting) for quite some time, California has recently released their own green building directory and map. The green building directory is searchable according to location, LEED rating and status, project owner, and the inclusion of energy efficiency projects.

Andrew Turner of HighEarthOrbit and Mapufacture, Inc blogged about the state map a couple of days ago. He converted the data into a KML file, which is available from the post for those who wish to create their own map from the data. He developed a revised map based upon the data. This revised map easily sorts the buildings according to LEED certified buildings, buildings pending LEED certification, an other category, and those buildings under 10,000 square feet.

For those interested in learning more about the economic valuation of the environmental benefits of green roofs, Environmental, Science, & Technology released a paper that I co-authored on the topic. “Green Roof Valuation: A Probabilistic Economic Analysis of Environmental Benefits” summarizes the benefits over the lifetime of a green roof taking into account benefits due to energy savings, reduced stormwater fees, and potential savings under market-based valuation of air emissions uptake. This is presented in a probabilistic manner to aid decision-makers when considering a green roof or policies to encourage green roof adoption.

The energy literature on green roofs developed in the 1990s. The majority of research has focused on the insulative abilities of green roofs in summer. In summer months, green roofs behave as high quality insulation reducing the flux of solar radiation in a building [1,2]. Insulation layers may retard heat flux in situations that are undesirable. While insulation reduces cooling load for hours when outside temperature is higher than inside temperature, the insulation retards heat loss for those hours the internal temperature exceeds external temperatures [3]. For a dark roof, the negative impact on AC usage during hours where external temperatures were below internal temperatures was greater than for a white roof suggesting that both roof insulation and roof reflectivity should be assessed to minimize energy use in buildings.

A recent study on the surface heat budget on a green roof and high reflectivity roofs revealed that the sensible heat flux is small compared to concrete roof surface on both a highly reflective white paint surface and a green roof [4]. The heat flux is small on the white roof due to the low net radiation. In contrast, the green roof had a large net radiation. The small sensible heat flux for the green roof was attributed to the large latent heat flux by evaporation [4].

The two main parameters that influence the solar radiation that reaches the roof deck are leaf foliage and soil thickness. The leaf area index (LAI) and leaf angle affect shadows [1]. The larger the foliage development of a particular plant, the smaller the heat flux through the roof [1,2,5]. Roof surface temperatures also decrease according to increasing LAI [6].

Soil thickness also plays an important role in heat transfer. Thick soil layers reduced cooling needs during summer months while thin substrate layers resulted in little to no cooling benefit [5]. Roofs with substrates between 7.5 cm and 10 cm reduced the average daily heat flow throughout the year although greater in summer months [7]. Generally, heat transfer is greater on roof surfaces that are not vegetated [2,6] although the vegetated roof should not serve as a replacement for insulation [8].

Sources:
[1] Del Barrio, E. 1998. Energy and Buildings, 27:179-193.
[2] Niachou, A; Papakonstantinou, K; Santamouris, M; Tsangrassoulis, A; Mihalakakou, G. 2001. Energy and Buildings, 33:719-729.
[3] Akbari, H. 2003. Energy, 28:9:953-967.
[4] Takebayashi, H and M Moriyama. Building and Environment, Volume 42, Number 8, p.2971-2979.
[5] Theodosiou, T G. 2003. Energy and Buildings, 35:909-917.
[6] Wong, N; Chen, Y; Ong, C; and A Sia. 2003. Building and Environment, 38:261-270.
[7] Liu, K; Minor, J. Proceedings for 3rd Annual Greening Rooftops for Sustainable Communities. Washington, DC.
[8] Eumorfopoulou, E and D Aravantinos. 1998. Energy and Buildings, 27:1:29-36.