Friday, December 18, 2009

More Solar Access in Denver

Chris Kennel, a thoughtful resident of Southeast Denver, recently submitted his thoughts to Doug Linkhart on the solar access issue:

"At the Thursday Nov. 19 council meeting I spoke with some advocates of solar access because I plan to install a photoelectric array on my roof and am curious about their ideas. Every solar access advocate I spoke with seemed well-meaning, but I didn't find that any of them had thoroughly considered the implications of their plans. That is why I have chosen to write this letter to you.

The four types of solar access that I heard the solar access advocates describe were:

1) passive solar (sunlight entering windows of their homes)
2) solar hot water panels
3) gardening
4) solar electric (photovoltaic) panels

Each of these solar uses functions differently at different times of the year and therefore has different requirements in terms of access to the sun. This means that a one size fits all approach would either not address each area appropriately or be totally overkill for some areas.

Lets look at each area, starting with the most restrictive one: passive solar. Passive solar, used for heating and lighting is most beneficial when the sun is low in the sky in the winter. In the summer, passive solar is unwanted since it adversely affects indoor comfort and raises the cooling costs of a home. If people want direct sunlight in their first story windows during the winter months, then it
would preclude the design of most of our existing city blocks. In the morning during the winter months, the sun is so low in the sky that an object 2 feet high will cast a shadow 10 feet long at 8 am in the morning. At noon, when the sun is highest, the same shadow would be created by an object that's about 5 feet tall. This means that if someone has a window on their first floor, the roof or gable of neighboring single story house that's 10 feet away to the south would very likely shade its
neighbor to the north. To get unobstructed winter light into a house at noon would require the neighbor's house to be located at least 20 feet away if it's a single story. For morning light, the neighbor would have to be about 40 feet away, and this gets even larger if the southern neighbor's home is a two story.

The second most restrictive solar access issue is rooftop solar hot water panels since these are often used for winter heating. For solar panels, the sun is most effective between 10 am and 2 pm. Two single story houses would be fine close to each other as long as the southern neighbor doesn't have a gable facing the north neighbor. If the southern neighbor has a gable or a second story it would
have to be about 26 feet away from its single story neighbor to avoid shading the rooftop panels during part or all of the 10 am to 2 pm timeframe. If the southern neighbor has a two story gable roof facing the north then it would have to be about 40 feet away.

The third most restrictive solar access issue is gardening. This activity usually happens during the summer months when the sun is higher in the sky, and most sun-loving plants like tomatoes require about 8 hours of sunlight per day to thrive. A single story house would cast a 15 foot shadow and a 2 story house would cast a 25 foot shadow during parts of this timeframe. For gables facing north add another 7 feet to these numbers. People with large lots should be fine, but narrow lots would
receive too much shade for the most sun-loving plants. People with narrow lots could grow plants that tolerate partial shade since from 10 am to 2 pm the shadows from the worst case scenario, a two story house with gable would only cast a 14 foot long shadow.

The most flexible solar access issue is photovoltaic panels. These panels function most effectively in the summer months when the sun is more direct and intense. During the winter months, their output is substantially reduced, so winter solar access shouldn't be over prioritized. Photovoltaics function best from 10 am to 2 pm, and it's unlikely that even a two story neighbor would shade the roof of a single story house to the north during this timeframe in the summer. The more likely
source of shading is from a chimney on the homeowner's own house or a tree. Photovoltaic panels have a weakness in that if any part of a single panel gets shaded, it knocks out the entire panel and in many cases the entire array or branch circuit. Even a leafless deciduous tree in the winter can cast enough of a shadow to knock out a photovoltaic panel. So if photovoltaic panels are given some special status with regard to solar access then it may result in severe tree pruning and even removal, especially to the city's larger and older trees.

Since trees have many benefits, it seems important to exempt them from any rules regarding solar access. Otherwise neighbors will be trying to trim the trees that other neighbors or the city (via parks and greenbelts) own. Even at my house I have some trees that cast shadows over 100 feet long during the winter months, and my trees are only medium sized. I live in a suburban neighborhood so these trees don't affect my neighbors much, but medium sized and larger trees in an urban neighborhood could conceivably cast shadows across four or more lots.

Although solar access sounds nice in theory, creating solar access rules in excess of our current bulk planes is certain to cause a lot of problems. For the group of of Denver residents who place a premium on solar access (and I am one of them), the best and easiest solution is to choose a site that has a park, street, drainage ditch, or other form of undeveloped open space to the south. A second option is to buy a house that's located on the northern most part of its lot.

Not all homes in Denver are equal in many regards, and solar access shouldn't be viewed as a right but rather as a feature. Although I might like my suburban house to be within 5 blocks of a light rail station, a park as good as Washington Park, a bike path, stream, and an excellent coffee house, I can't expect the city to give me all these things. Solar access is similar. Solar access is a function of location, topography, and the direction a home is pointed. As such it has value to some people, but it cannot be equal throughout all of Denver.

For people who do not want to move to a home that has good solar access, there are alternatives. Instead of photovoltaic panels, they can buy renewable power through Xcel energy's wind source program. People who want fresh, local produce can join a CSA (community supported agriculture), participate in a community garden, or visit the farmers' markets instead of planting their own gardens. If someone suffers from SAD (seasonal affective disorder) in the winter they can buy a light therapy box (my wife and I have one and it works great) instead of relying on passive solar light.
Lastly, people who want to reduce their heating costs can better winterize their homes as an alternative to using solar hot water panels or passive solar designs. Better winterization will also make a house more comfortable and energy efficient in the summer. All of these are good options for people who do not have the guaranteed solar access they wish for. It's likely that they've chosen where they live due to other redeeming factors.

Thank you also for your hard work on the rezoning project.

Chris Kennel"

Lots of good common sense from Chris.

Note: As Douglas Farr and myself have been advocating, the best place for your photovoltaic system is on a two story garage on the alley. Xcel energy is already trimming the trees back there to protect the power lines. The most likely source of shade will then be a pine tree to the south. Try to get an agreement with that neighbor to allow you to prune that tree as required. If he won't grant permission for free, offer some money for a solar easement. You'll eventually earn all that money back and more.

Saturday, December 12, 2009

Your New Zero Energy Cost Home Must Be All Electric

Xcel Energy currently charges $10.28/month just to hook you up to gas. That means if you do a great job of design and building, and drive your gas usage to zero, you still pay over $120/yr for the privilege of gas heat backup. You can install a huge PV or thermal solar system, but it won't eliminate that charge.

So the easiest way to get rid of it is to eliminate gas to the house.

For all you chefs out there who love to cook with gas, remember that it puts quite a bit of CO into your home. You may want to check out induction cooktops which reduce the chances of anyone burning themselves, and actually heat quicker and more energy efficiently than gas.

Friday, December 4, 2009

Solar Cats and Passive Solar Energy Collection

Did you ever wonder what the surface temperature is of your solar kitty?

As you can see, Natasha runs about 112F on a clear, cold winter day in Denver. Note: she is laying in front of a window with an SHGC (solar heat gain coefficient)of 0.56. That's far higher than the average low E window which has an SHGC of about .32. What's that mean to a cat? About 15F. A black surface in front of a conventional low E window under the same conditions is around 97F. Still warm, but that's a significant penalty for not specifying the right windows.

Hurd "hard coat low E" windows from Rocky Mountain Solar Glass has been the only local solution I have found for passive solar. Serious Windows (formerly Alpen) should also be able to supply a high SHGC low E window. Most other window suppliers and manufacturers have no clue about this issue.

Increased solar gain in the summer isn't a concern, because these are south facing windows. In the summer, the sun is high in the sky, and the window is completely shaded by the properly designed overhangs. Even the Energy Star program is silent on this, although their energy modeling computer programs do give credit for high SHGC windows on the south side.

Tuesday, December 1, 2009

LED Lighting in 2009

Here's a photo of the aforementioned lighting "hack".

It took 15 of the 1.5 watt LED bulbs to generate enough light for this kitchen remodel. Current cost: $4 each.
This configuration will use about eight times less electricity and save about $45 per year, including replacement costs. That's a 16 month payback.

Saturday, November 21, 2009

Druid Zoning

Denver's new zoning code is on track for approval in February, after about five years of hard work. In the last few days, many folks have rallied in support of "passive solar access". It's a big enough groundswell that it has gotten everyone's (except the Mayor's) attention for the moment.

At first blush, it sounds like a great idea, but only one person has attempted to quantify what it really would require in terms of zoning.

Bernadette Kelly of MOA describes "block sensitive height limits" as a solution. Similar to how the context sensitive front setback is calculated, it would regulate building heights based on the current status of what's on the ground. She cites an English "right to light" law that derives from the Druid civilization. To paraphrase: "if a structure has had access to the sun for at least 20 years, it is illegal to ever block the sun from that structure".

It does solve the problem, would satisfy most solar advocates, but it is a bit impractical to implement, and would greatly diminish your neighbor's current property rights. (Full disclosure: the author is a solar advocate, but hopes to profit from the ability to increase density in transit neighborhoods)

It's doubtful that this proposal will see the light of day in this version of the zoning code, but it's not without merit. Some neighborhoods of one story homes and large side setbacks may want to STAY neighborhoods of one story homes and large side setbacks, and there are no tools in Zoning Code draft 3 to help preserve that context. Two story homes have always been allowed everywhere in Denver, and CPD has thus far refused to change that.

Saturday, November 7, 2009

The Rubber is Starting to Meet the Road for Smart Grid City

The Smart Grid pilot project in Boulder is now well enough along for the peak period re-pricing to be released.

This article missed answering an obvious question:

If you own a PV system that contributes to the grid during peak periods, will Xcel credit you at the higher peak retail rate?

My guess is yes. It's only fair. But this issue should be openly addressed soon because it will make your PV system pay off much quicker

Friday, November 6, 2009

LED Lighting Update

Yes, CFL's suck.

So, we've been waiting for bright, affordable LED lighting to become available. Sam's Club has recently introduced 1.5W LED bulbs for $5 each. I believe Xcel energy is subsidizing some of this cost based on a flyer displayed in the aisle. If anyone knows more about that, please post a comment.

Anyway, 1.5W is only producing about 78 lumens, which means you'll need roughly six times the number of bulbs more than "normal". This is a daunting problem that will keep most folks out of the LED replacement business until a market solution or even brighter bulbs are introduced.

In the meantime, we developed a hack using "Medusa" floorlamps, which can be found for as little as $20 and will convert a standard octagon ceiling box into a fixture with five medium base openings. An added bonus is that you can direct the lighting to where you need it.

Let's say you have rentals or are doing fix and flips. You already know that fluorescent lighting and CFL conversions do NOT add value, even though operational cost is lower. The light quality of LED's and even lower operational costs SHOULD add value to your project. Don't be cheap - the $20 marginal cost per fixture is only a couple hundred $ for a house.

Edit: photo posted above

Monday, November 2, 2009

Dual Flush Toilets Now Affordable

If you've been too cheap (like me) to get a Toto or Caroma Dual Flush Toilet, now you have no more excuses. For a long time, these toilets have averaged $400, making them difficult to pay for themselves.

Sam's Club is stocking the Alexis HET (high efficiency toilet) 1.1 gpf liquid, 1.6 gpf solid dual flush toilet for $99.

Since Denver Water is giving a $125 rebate for them, this is a real no-brainer.

Go get one while they still have 'em.

Wednesday, September 23, 2009

Solar Shading Cont'd

The classic all-aluminum rollup design is my personal favorite solution for exterior window shades. They're economical, ( $150-$300), self-storing, accessible from inside the home, and infinitely adjustable depending on the season or your whims.

They can be ordered at Home Depot or online at

Wednesday, September 16, 2009

Sun Control - One of the Solutions to Summertime Overheating

This topic is old news for those of you with those big, west-facing-mountain-view windows. They create an inferno for you in the summer. You may have even spent thousands on beautiful floor to ceiling blinds to shut out the sun.

However, unless the shades are physically outside the window, they are relatively ineffective. Once the sunshine comes in the window, it stays inside as heat.

So the shades must be on the outside.

The easiest, quickest, and least expensive way to install an exterior window shade without completely ruining the view just might be from Screenmobile. They are a national franchise, and I've used the local branch often for conventional screen replacement, and found them to be a good solution for an annoying problem.

Friday, August 28, 2009

Heat Pump Hot Water Heater

So, you're trying to decide how to heat the domestic hot water in the zero energy house you are designing for Denver.

Solar hot water heaters are an excellent choice. However, the logistics of a solar thermal installation are daunting compared to a typical appliance installation.

A logistically easier solution is to use a heat pump water heater (HPWH) in conjunction with PV solar.

Rheem has just released a new nice-looking unit.

The jury is still out as to which configuration will be best. Recent test results and common sense are beginning to favor HPWH with PV. The reasons for this are that solar DHW is insufficient and inefficient in the winter, and underutilized in the summer. A grid-tied PV system has the advantage of constant efficiency and 100% utilization year round. In addition, large PV cost reductions are coming, but none are expected in solar thermal. State-of-the-art solar thermal collectors still use supply-restricted copper, aluminum, and glass. The labor content of solar thermal installations is also quite high.

Some puzzles remain with the implementation of HPWH systems. Per the manufacturer's recommendations: "Because the heat pump’s exhaust air is cooler than the surrounding atmosphere, these water heaters generally do not belong in or near busy living areas of the home." Since they pull the heat out of the surrounding air, a small, airtight mechanical room isn't the best place for it either.

Discussion of HPWH locations:

1. The garage. A new, well insulated garage might work. An uninsulated garage slab gives off enough low temperature free geothermal heat* to prevent freezing of the pipes to the heater. There are at least two problems with the garage, however: 1. In summer, the HPWH gives off cold air that would be more desirable inside the living space than in the garage. Ducting air from the garage to the house is a CO hazard, and not recommended. 2. If the (insulated) garage door is inadvertently left open in the winter for an extended period, the water lines to the HPWH are at risk of freezing.

2. Mechanical room with forced ventilation. The control scheme and ducting layout for this ventilation can get complicated and costly.

3. Basement. This is where you usually find the water heater in new construction, and will work just fine if you don't mind a cold basement in the winter. If you finish the basement and add heat to it, that heating system will be feeding the HPWH the heat it needs, and this will spoil the overall efficiency of your system.

"The House as a System" philosophy of home design will get a real workout on this one. Please enter a comment if you've heard of any other solutions.

*A perimeter insulated slab in an insulated garage gives off 5-15 Btu/hr/ft2, based on preliminary research. This is a great match for a 7000 btuh HPWH.

Tuesday, August 18, 2009

The Greenest Building is Usually the One Already Built, but Not Always

I'm really not trying to anger preservationists or tree-huggers here, I'm just analyzing a trite slogan from an engineering perspective. I'm a pragmatic preservationist.

The question is whether or not you should rehab and do a green retrofit on an existing building or replace it with a well-designed low energy new building. The correct answer can only be found after making some reasonable assumptions, cost estimates, and estimates of resale value.

You don't "waste btu's" when you tear down an old building. Those btu's were spent when the building was originally built, and there's nothing you can do to get 'em back.

You can only choose not to spend new btu's on a new building.

And btu's are just another form of dollars.

So it's always an economic problem, eg., what's the present value of retrofitting the old building vs. building an entirely new one. This analysis must be done for every building using each case's unique problems and assumptions.

In residential at least, it's fairly easy to build a new "zero energy" replacement house, but fairly hard to retrofit an old house to zero energy. The cost of the new house can be estimated pretty accurately, but trying to estimate the retrofit cost of the old house is risky. Every old building is different.

The embodied energy of the new building is just part of the down payment on a really good investment. The value of that energy is in the cost of construction. The landfill space required for the old building is also given a dollar value in the cost of demolition. The embodied energy of the old building is a "sunk cost" and doesn't factor in the analysis.

The main thing that doesn't have a dollar value in this analysis is the generation of CO2. Lawmakers have begun trying to put a dollar value on that. Eventually this "carbon tax" will be pretty accurate, and will favor the old building.

Most estimates put the embodied energy of a new building at 5-15% of the lifetime energy usage of the building. That means the operating energy usage of the building is about ten times more important than the original energy content.

Therefore, it may be a catchy phrase, but it's very unscientific to generalize: "The Greenest Building is the One Already Built". Be sure to say "usually".

Thursday, August 13, 2009

Mini-Splits or PTACS are the Key to Net Zero Energy Homes

High SEER minisplit heat pumps have finally caught the attention of high efficiency homebuilders. Postgreen, a redeveloper in Philadelphia, touts "geothermal efficiency at a fraction of the cost":
When you add PV solar to a house and a high efficiency and lo-temp-capable heat pump, then you really don't need to pipe natural gas to the home. (Cooking meals with gas may be preferred by chefs, but it is neither healthy nor energy efficient. Gas ranges put out a lot of CO). That saves the $12/month gas hookup fee.
Besides, you can't send natural gas back to the utility the way PV solar sends electricity back . In superinsulated homes, this scenario also makes solar thermal obsolete for heating and domestic hot water (DHW)
Why? Because even at a solar conversion efficiency of only 10%, in the summer, you are putting energy back on the grid and dollars in your pocket Every. Single. Day. Thus, the yearly system efficiency and ROI is better than solar thermal.
It's becoming accepted worldwide that the only way to acheive true net zero energy is with an all-electric house and PV. Minisplits are part of the puzzle.
A few more of benefits of these heat pumps:
1. Less floor space used inside the house for mechanicals.
2. Compression-cycle air conditioning included "for free".
3. Better zoning is possible than with any sort of central forced air system.
4. In smaller homes, the installed cost is a fraction of a centrally ducted system.

Sunday, July 19, 2009

Denver's New Zoning Map is Dropping the Ball on Sustainability

Soon after being named in the top ten cities for sustainability , Denver may damage it's standing because the proposed new zoning code is largely ignoring the benefits of detached accessory dwelling units (dADU's).

First, a little history:

The zoning code rewrite was called for as far back as 1989. Mayor Hickenlooper hired Peter Park to shepherd it in 2004. Meanwhile, preservationists like Jim Lindberg were concerned how the old code was allowing redevelopers to potentially ruin our historic neighborhoods. Blueprint Denver was begun in about 1998 and released in 2002 as the guide for a new code. The Zoning Code Task Force (ZCTF) was appointed in early 2005, consultants were hired, problems identified, and neighborhood contexts were defined.

Along about early 2008, third parties realized that sustainability issues had been heretofore largely ignored by city staff and their consultants. Michael Henry and Don Tressler of INC (InterNeighborhood Cooperation, an RNO), are the most significant of these third parties. Although Greenprint Denver was initiated in 2006 and widely admired, it was two years before Greenprint representatives were spotted at any ZCTF or Blueprint meetings.

At the request of INC, Park then hired Doug Farr to recommend sustainability strategies for the new code. The author wonders why a Chicago based consultant, however well qualified, could be a better choice than a local firm. For example, does Farr know why evaporative coolers are such a great peak power solution for the Denver area? Probably not. It turns out that swamp coolers ARE a zoning issue. No matter, he wrote the book, and made an effort to interview local experts like Michael Tavel.

Also, in the spring of 2007, Bob Sperling and James Van Hemert  and myself organized the Friends of Granny Flats after we realized that the Zoning Code Task Force was almost unaware of the existence and popularity of thousands of historic carriage houses in Denver. We gave a presentation to city staff in April 2007 that was well-received and put dADU's on the radar.

Farr gave his report to the ZCTF in September 2008. At that meeting he was asked, "what are the biggest things we can do in Denver?" His reply, "Two things: Share cars and Solar Access". It looks like the private sector is already targeting the former. By solar access, he went on to explain, on north-south Denver streets it means allowing a taller garage with solar panels on the roof, with laws to prevent future shading of it. After the meeting, he took the concept further and proposed, "for sustainability reasons, the code should require the installation of an accessory dwelling unit whenever these alley structures are built."

(Coincidentally, at the same meeting, the housing affordability consultant, Don Elliot, was asked the same question. His reply, "ADU's, reduction of the minimum buildable lot size, and inclusionary zoning." The ZCTF took the first two choices to heart and they are well-represented in the draft code. The affordability recommendations promised ADU's "in a wide range of districts." The efficacy of Denver's current inclusionary zoning law is unclear.)

After staff parsed Farr's report, they issued the Jan. 14, 2009 sustainability memo , and ADU's are prominent. Mention is made of future study of things like solar fences, kind of a tough putt in urban neighborhoods with mature trees. More on that here and here.

Unfortunately, the proposed zoning map is disallowing ADU zoning over most of the city.

Review the Map . Look for suffixes like -B1, - C1 etc. For example, if your neighborhood has U-SU-C you don't get ADU's, but if you have U-SU-C1, you get 'em. B2 & C2 zoning allows them only on some corners, which is better than nothing, but there isn't any B2 and C2 on the map. Why develop a zoning typology and then shelve it? There are a lot more questions like that once you study the map. Please do, and weigh in .

So, in 2009, after all this work, why is the city offering up ADU zoning in less than 5% of the city?

Edit: As of late August 2009, the areas with ADU zoning shown have increased, but they are still insignificant. There is a small amount of A2, B2 and C2 now shown.
Edit(2) As of November 2009, there is tons of ADU zoning shown. Meanwhile, "Friends of Granny Flats" recommended ADU zoning for ALL single family districts.

Tuesday, April 14, 2009

Solar Access for Denver Neighborhoods

The Denver Zoning Code has been rewritten, and is on the verge of release for public comment. The issue of Solar Access has been put on hold for at least a few months. This is understandable, as the release of a large, important document like this is very difficult.

Unfortunately, solar systems are being built in Denver with no protections against shading from neighbors.

For more, please see read this document:

Solar Access for Denver Neighborhoods

Friday, March 27, 2009

Connecting the Dots Between Google and the Smart Grid

How the Google Math Adds Up:

1. Google is rapidly becoming the nation's largest single consumer of electrical energy.

2. 2007: Google announces their goal of producing renewable (solar) electricity as cheap as coal. The goal: $ 0.025/kwh

3. Plentiful solar electricity is generated during the common peak demand periods, hot summer afternoons.

4. 2009: Google announces the PowerMeter to help implement the "smart grid" as they envision it. A properly implemented smart grid could increase the selling price of peak demand power to $ 0.25/kwh or more.

Therefore, #4 causes a 3x to 10x increase in the profits of #2, while #3 + #2 solves problem #1.

The Return of the Carriage House, Denver 2009

Detached accessory dwelling units will apparently be allowed in Denver's new zoning code. The sustainability benefits are so numerous that ADU's tend to be the darling of city planning staffs nationwide.

The following article was written by Becky Alexis, a Platt Park architect involved in sensitive redevelopment.

"The carriage house has been a part of our built environment since the beginning of the twentieth century. Found everywhere in our community from Country Club homes to low income areas, the accessory dwelling unit has historically provided home owners needed flexibility for guests, expanded family, boarding and household help. Today our need for a sustainable housing sector is eased if home owners have the same opportunity. By converting the rear zone of a property into the highest and best use, families, neighborhoods and municipalities benefit socially, economically and environmentally.

Giving home owners the opportunity to add functional value to their property helps all socio-economic levels. From the first time home buyer to the elderly, the added dwelling space helps all owner-occupants to stay in their home. Fabrication is less costly than conventional housing and uses include family living, child and elderly caregivers, workspace and rental income. This flexible space affords opportunity for families’ changing needs in a time where the risk of home loss is high. As a work space, the detached dwelling reduces costly commuting requirements. The building form adds security and beautification to the alley and creates intimate and properly scaled courtyards which require less water and maintenance needs. Simply, the carriage house aids in preserving single family living.

Keeping families in their home is critical for the stability of neighborhoods. Less housing turn-over means less speculator driven scrape-offs, and a preservation of the neighborhood character. The added benefit of a carriage house to a property increases the value of other homes in the area. The added activity also reduces crime, especially in the most vulnerable space, the alley. Conceived as 800-1200 s.f. apartments over a 2-3 bay garage, these units reduce existing and future off-street parking demand. Safety, secured property values, and an improved built environment make the neighborhood more livable and desirable for existing and new residents.

To the municipality, this non-obtrusive densification of our neighborhoods has numerous benefits. The existing utility infrastructure is currently under utilized, so adding more dwellings would be accommodated and would add a larger tax base to support the existing infrastructure. Families would not be financially forced into the suburbs. Children could stay at their schools. Commuting by vehicle would be minimized, and our local public transportation would be better utilized. Jobs would be created by the people that build these structures and by the folks that choose to work out of them. It is a win-win situation that reduces stress on families, reduces falling house prices, minimizes scrape-offs which fill our landfills, reduces water needs with more sensible backyards, and reduces our carbon footprint.
Denver’s own Peter Park, the City Planning Manager, has said, “When cities stop changing, they start dying.” This is a “Shovel-ready” opportunity for good design and correct context to fulfill real and perceived needs."

-Becky Alexis, HIVE Architecture, LLC

Thursday, February 26, 2009

Polymer ISC Solar Collector Debuts

Just a few days after my post about passive solar thermal water heating, the grandson of the Arthur D. Little collector design came to my attention. Called the Solar Cache by Harpiris Energy, it has been designed only for non-freezing climates. With PEX pipe, which may be considered freeze tolerant, this will be a great product for economy installations, costing far less than the usual $6k solar DHW systems for freezing climates.

I just hope it doesn't get installed in colder climates, freeze, burst and give the product a bad name. When drain-down systems were used in Denver in the 80's, many an attic was flooded because of Murphy's Law. Even though there were freeze protection controls and backup freeze protection controls, they still failed.

Ironically, a common complaint from solar DHW system owners may cause pumps to appear in these passive systems. See, most systems have a solar preheat tank (with the Sun Cache the solar tank is on the roof), and a backup (fossil fuel) tank piped downstream in series. If the homeowner doesn't consume any hot water (like all day when he's at work) then the backup tank fires to make up for standyby losses, even though the preheat tank may be 140F or higher. In the summer, a solar system should be providing 100% of the hot water load on sunny days, so some homeowners get peeved when their gas bill isn't zero and the backup tank is coming on every hour or so. A really tiny recirculating pump with a simple control is a way to prevent the problem, but now you've added a pump to an otherwise elegantly simple system. The other beef with the "uninsulated" storage tank on the roof is that you'll never have any solar hot water left for the morning shower, the storage water will drop close to outdoor ambient by morning.

Rheem has also come out with a passive collector with some freeze tolerance. The collector loop is charged with antifreeze. Again, great care should be used on the supply pipe, even in "non-freezing" climates.

Sunday, February 8, 2009

Hail Resistive Roof Saves on Insurance

State Farm just started putting this line on my insurance declaration page:

Premium Reduction:
Hail Resistive Roof: $521/yr.

My roof is a spanish tile look-alike made of stone coated steel from Gerard

I don't know if clay-based or concrete tile roofing qualifies for the discount, which is about 30%. Both of those systems, however, require a significantly stronger roof structure due to the higher dead load. (edited 2/10)

So, I got a premium-looking roof that pays for itself in ten years compared to asphalt shingles.

It's a very green choice because the steel is recyclable, and guaranteed for 50 years.

Friday, February 6, 2009

Green Roofs?

I have remained on the sidelines with regard to promoting green roofs. I'm hesitant partly because many people in the multifamily industry have this saying that goes "flat roofs always leak".

In my own experience, the most frequent and worst leaks occur at the low spots where ponding occurs. A pond on your roof causes dust in the air to stick to the surface of the water. Over time, this dust builds up and starts looking like dirt, or soil. Seeds get blown into this muck, and sprout. I know this is a poorly designed ad-hoc green roof, but the fact remains that leaks never start in the dry spots on flat roofs.

I guess some sort of roof garden would be nice if you also had a roof deck and actually used it.

I'll let Dr. Joe L., every building scientist's hero, explain it:

"Green roofs? Grass and dirt are not energy efficient.Work with me here. Which saves more energy—2 inches of dirt or 2 inches of insulation? Which saves more energy—grass or a white colored membrane? Which is more expensive and does not save energy—grass and dirt or insulation and a white colored membrane? Which needs to be watered to keep the grass from dying and blowing away? But they are beautiful and look cool. And that apparently is more important than cost and energy savings. Okay, I can live with the beautiful and looking cool argument if that is in fact the argument—but don’t clutter it with half-truths such as heat island effects and water run-off. There are other (better) ways to deal with each."

He goes on to admit he won't win the argument, so he provides the proper drawing detail that works.

In semi-arid Denver, I'll posit that the money spent for the water needed to keep your roof alive will be far more than the dollar value of any perceived benefit.

Thursday, February 5, 2009

Passive Solar DHW

To some, the holy grail of solar thermal is a system without pumps and controls.

Himin of China manufactures a nice one:

At Solaron in the '80's, we purchased the manufacturing rights to a passive DHW design developed by Arthur D. Little. The problem was that the pipes going to the collector would freeze in the winter. Frozen pipes in the attic were so undesirable and difficult to eliminate that we ultimately abandoned the whole project. As far as I know, no one is pursuing this type of design in northern climates.

Now that building codes are beginning to actually recommend insulated roof planes and conditioned attics, the Chinese design looks very interesting. The pipes in the attic won't freeze because the attic is inside the house envelope. As long as the piping to the roof-mounted tank is kept extremely short, it won't freeze either. Natural convection within the pipe and heat conduction along the pipe from the tank and the attic area would prevent freezing.

Note that the water in the evacuated tubes probably won't freeze.  Every day they warm up a bit even if the day is completely overcast.  This insolation should be enough to prevent freezing even under the worst conditions in Denver.

From Arthur D. Little, we also learned that the roof-mounted tank will never approach freezing temperatures anywhere in the continental US. (Basically there's enough solar insolation even on completely cloudy days to keep the tank above 40 degrees)

The main attraction of this design is that system efficiencies are far superior to pumped designs. Also, with no moving parts to fail, the life-cycle cost is held low, and the ROI is maximized.

Edit, corrections 1/10/11 (the tubes contain water, not heat pipes.)

Friday, January 23, 2009

It's Not Price-Pfister, but the "P" is Silent

In a recent trip to the Wellington Webb building, a had a chance to use my first waterless urinal. I don't yet know how they work, but it was totally odorless and splashless, all in all very pleasant.

If your household has at least two guys, you should install one. The water savings will eventually pay for it.

Update: About six months after installation, I visited the restroom in the City and County Building, and one of these urinals was malfunctioning somehow. It was NASTY. Caveat Emptor, and train your maintenance staff!