Monday, June 18, 2007

Draft Greenprint Denver Residential Design Manual

Kevin Dickson 2007

Green building is VERY climate/site/zoning/architectural program specific, so Denver needs these specific recommendations to guide design. This draft addresses sustainable homebuilding in the City of Denver with its specific zoning and building codes.

It should be noted that when Quick Wins eliminated Denver's solar bulk plane, there have been few incentives for incorporating solar energy into home design.

  1. Photovoltaic systems are currently preferable to Solar Thermal and Passive Solar. There are many reasons for this, but a few of them have been addressed in comments by Mark Eatherton, one of the country’s most experienced and innovative hydronic and solar heating system contractors, who just happens to practice right here in Denver.

In his words, “But for the mean time, at least here in Colorado where the utiity is REQUIRED to buy back excess electrical production, I'm thinking PV solar makes more sense for the world as a whole. If during the summer months, the dwelling to which the array is attached can not use the electricity being produced by the PV system, it goes back into the grid, helping to offset the demand imparted to the grid from cooling loads.”

When taking this idea further in the R-2 zone, you discover that new construction duplexes don’t lend themselves well to solar. We should allow 22’ wide 2.5 story homes on 25’ lots. Gabled roofs would be the preferred solar configuration. PV cells would be on the south side, silver galvalume metal roof on the north side (see photo). The silver metal is designed to reflect sunlight onto the PV cells of the adjacent house, nearly doubling their electrical output. Optionally, an unglazed thermal collection system such as Dawn Solar or Warm Board could be integrated underneath the PV cells. This thermal energy would be 100% of the domestic hot water load on all sunny days above 40 deg. F.

  1. Ten Percent of the homesites in Denver are excellent candidates for Passive Solar. The side of every lot on the south end of north-south blocks has unobstructed sun. One way to get the word out is to require a consultation with Greenprint Denver’s Passive Solar consultant whenever a zoning application or demolition permit is filed for one of these lots. Edit: As the older neighborhoods get redeveloped, this ten percent could be increased to a potential 30%+ if zone lots on both ends of the block were allowed to be reconfigured in this manner facing south on the avenues:

  1. More incentives needed. City government financial aid helps get the word out about sustainable best practices. Builders are always very slow to adopt new technology because they’ve all been burned by it at some point.

  1. Reuse is better than rebuilding?. Jim Lindberg recently stated “The greenest home is an existing home”, i.e., tearing down and rebuilding isn’t as green as retrofitting the old home. This could be true in many cases, but the concept needs more scientific analysis. A usable basement is high on Denver homebuyers’ wish lists, and a basement retrofit is still financially unfeasible.

  1. Pick one green rating method. The Denver Building Dept. needs to recommend one house rating method among the many. With a little research, we could determine which one gives the best results for Denver’s climate, and is the most user-friendly. All these methods are continually being updated, so using just one means that consumers will be able to compare apples to apples. (This has been addressed in the Climate Action Plan)

  1. ADU’s are picking up steam. Carriage homes and granny flats solve a myriad of problems without creating any. If they are allowed through a change in the zoning code, they should be promoted as a green feature. The roof of a new 2.5 story carriage house is the single best place for a solar photovoltaic system.

  1. Rebuilding existing neighborhoods is far greener than contributing to sprawl by building new subdivisions. Denver has this intrinsic advantage over outlying suburbs. Perceived lower housing costs in the suburbs are offset by higher transportation costs. This point needs to be stressed to young families headed to the cul-de-sacs of Highlands Ranch. Stay in the city and build an addition if necessary.

  1. Superinsulation in new construction and retrofit should be promoted. "The Super-Insulated Retrofit Book" states that you can cut heating requirements about 75-85% on most houses with pre-1970's style insulation (these houses had very little insulation because energy was so cheap). Although IRC requires a high R-factor, stud and header losses even with 2 x 6 construction are high, so a thermal break should be required. Our research has not yet revealed the ideal way to retrofit historic brick homes. Thermally, EIFS is excellent, but you have to turn a brick house into a stucco house, which is not usually a desirable scenario. A “thin brick” veneer brings back the brick look and near-zero maintenance, but doubles the cost. Injecting foam between brick courses is helpful, but achieves R-8 at best. IRC 2006 requires R19 walls. Low e paints should be investigated, inside and out. If the wall is brick veneer on concrete block, the voids in the block should be filled with insulation.

  1. The vented attic is dead. Building science for Denver’s climate prefers conditioned attic space. Add just a couple feet to the attic kneewall, and now you have a cheap and charming bonus room. Vented attics developed mainly because homes leak a lot of air, and water vapor condensed in the cold attic. Venting then became the only way to dry them to prevent rot. The summertime performance under this scenario is even worse, energy-wise. IRC 2006 provides this new conditioned attic detail.

  1. Energy efficient homes and/or homes near transit can qualify for better mortgages. The lenders understand that the buyers will have lower transportation costs. Most families could give up the second or third car.

  1. There should be some financial incentives for TOD in selected areas of change. Maybe a break on property taxes for a few years.

  1. Heat Recovery Ventilators are required by code in Canada. Some local builders are accomplishing the same fresh air supplementation by a simple bath fan that runs 24/7. If HRV costs are reasonable, they should be utilized to recapture the heat in the exhausted air.

  1. Builders need training and encouragement to use evaporative cooling. Edit: Denver City council passed a law to encourage evaporative cooling and discourage central air.

    1. One of the best green builders in the state has told me that he’s afraid to introduce water vapor into a home for warranty reasons. Even though that’s overreacting, a local company, Coolerado, has already solved that problem.
    2. Another reason swamp coolers aren’t used is because they aren’t supported by national HVAC suppliers like Lennox.
    3. Low first cost, and low operating cost. This happy concurrence is rare in mechanical appliances. Sam’s Club price for a 4000cfm unit is under $400.
    4. Many of us Coloradoans with dry sinuses prefer the extra moisture all summer.
    5. Contributes to Global Cooling. On hot days, incoming air is 80F-100F, but the exhaust air is vented from the house at 75F. Conventional A/C units dump huge amounts of hot air into the neighborhood. That’s roughly three times less waste heat into the environment.
    6. To reduce maintenance headaches, they CAN be installed inside, in a vented basement mechanical room. (CAVEAT – this mechanical room MUST have only direct vent gas appliances).
    7. Barometric vent dampers will reduce window management. These dampers are simple, but not readily available yet.

  1. Denver has made a $6 Billion commitment to mass transit. Any R-0, R-1, or even R-2 (low density) zoning should be re-examined within 1/2 mile of a rail stop. The city and the citizens want a return on the light rail investment, and to get cars off the street. Higher density helps accomplish the goals. Neighborhood organizations will always initially oppose this, but Greenprint will start the learning process that higher density near transit is INEVITABLE. Fear of density is still all too common. New York City uses the 50% of the resources per capita of any other city because of density-related economies of scale. Similarly, we can learn from Paris. The typical building is six stories with no front setback. Are the neighborhoods charming? Yes. Is it easy to get around? Yes, but not so much in a car.

  1. Ground source heat pumps are still too expensive for low energy homes. Because of high initial cost, GSHP systems aren’t cost effective for low energy homes under 30,000 BTU/HR design heat loss. The equipment cost won’t be recovered before the equipment needs replacing. Centralized geosystems, however, always make sense in larger multifamily projects and possibly in a neighborhood-wide application.

  1. Use concrete commercial floor systems to increase thermal mass. This could increase comfort, reduce noise, and stabilize temperatures without increasing cost. As part of an overall strategy, this thermal mass can help save nighttime "free-cooling” for daytime. Other thermal mass systems are possible, such as double-drywall systems.

  1. Hot water recirculation BAD, on demand systems GOOD. It takes wasted water and wasted time for hot water to reach far-flung bathrooms. Recirc systems are more wasteful and expensive than on-demand pumps.

  1. Wind Energy. If the site has a good wind regime, these are usually much more cost effective than PV. Denver, however, has relatively little of the steady winds required. Xcel is investing heavily in large, high efficiency wind turbines, and passing the cost savings to us anyway. (Note: The Mercury CafĂ© has installed two wind generators near the CBD, so let’s keep an eye on their performance before we completely rule out micro-wind for Denver.)

  1. Smart meters and time-of-use pricing for all homes. Electricity that is consumed in the middle of the night (think off-peak thermal storage systems) should be much cheaper than electricity used in the afternoon of a hot day. Similarly, homeowner-generated PV electricity sold back to Xcel on summer afternoons should cost Xcel MORE than the average rate. Note that the old off-peak demand rates from Xcel were recently discontinued after 30 years because of lack of interest. Let’s not reinvent the wheel that no one wanted. (Originally called “off-peak” rates, then “time-of-day” rates, they were structured poorly and no conventional residences could benefit) Edit: Xcel, on its own initiative, has begun a smart grid city pilot project in Boulder as of March 2008.
This from the Leonardo Energy website:
"Italy is currently undertaking a programme to install 30 million smart meters. It is estimated that demand-side management tariffs, which limit customers to 3KW of power during peak periods, have reduced peak demand by 5% for 3 hours, 10 days a year. This has removed the need to construct a power station with 2GW capacity to cover the peak demand."

20. Keep an eye on LED lighting. The currently available bulbs are too dim and too expensive now, but they have good potential. The service life will be much longer than CFL's, and the light is more pleasing. Edit: LED's are now affordable, if still dim.

21. Greywater Heat Recovery is Easy. GFX Technology manufactures a heat exchanger that reclaims most of the heat from showers that normally goes down the drain.

1 comment:

  1. Yes, you would be a good neighbor, contributing to global "cooling", by shading your roof with with solar collectors, on the south and reflectors on the north! Global "cooling" means less air conditioning. Conventional home air conditioning, produces 3btu's of heat, in the environment to remove 1 btu of heat from your home. Shaded and "cool" roofs need less cooling, and they can produces electricity to help power your home and your evaporative cooling. Evaporative cooling takes 95 degree air, cools it 25 degrees, "breezing" through your home, removing home heat, and return it to the neighborhood at 75 degrees. 95 cooled to 75, equals neighborhood cooling! With home Solar PV (Passive Voltage) and a thermally efficient home, you can think globally, but heat and cool locally!