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.
Friday, August 28, 2009
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
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": http://www.postgreenhomes.com/models/
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.
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.
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
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.
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
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
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