Domestic Hot Water for Zero Energy Homes

Zero energy homes (ZEH's) in the near future will be simple, all electric, and supplemented with PV.

Hybrid PV/thermal solar collectors may be the best solution as costs come down. Sun Drum Solar is now offering a product. Dawn Solar also offers a building integrated hybrid PV roofing system. PVTSolar uses an air-based approach. When I worked at Solaron in the 80's, we abandoned air-based systems, and we were the world leader in air-based until that point. These are the only entries so far in the hybrid market sector. I expect to see more manufacturers enter the fray soon.

Whether or not a solar thermal DHW system is used, a grid-sourced backup water heater is required.
An affordable heat pump hot water heater (HPWH) is now on the market:
https://airgenerate.3dcartstores.com/index.html

This type of system uses only 25%-35% as much electricity as a standard resistance water heater, making it the best choice for a ZEH without solar thermal.
Another bonus of these heat pumps is that they can supply "free" summer cooling for the house.

In the near future as costs stabilize, we'll learn if this $700 is worth it for a home with solar thermal or hybrid collectors. In Denver, a home with 100-150 ft2 of solar thermal or hybrid collectors probably won't need it. The $700 marginal cost would take too long to recoup because the solar is providing 90%+ of the domestic hot water load.

More on Advanced Wall Systems

Joe Lstiburek was at the EnergyStar Summit this week, and was ranting about the wall system we should be using in this climate. Bottom line - for less money than than the historical R-13 2x4 wall system, you can build a styrofoam sheathed R30 2x6 wall. Truly a no brainer.

However, there are two significant barriers to implementation:

1. Your framers, who have such a difficult time coping with wall systems that use LESS wood.

2. Your structural engineer, who wants OSB sheathing used everywhere.

One slight potential problem within the assembly, vapor condensation on the inside surface of the styrofoam, has been bothering me for a few years. Joe explained that this has been addressed in IRC 2009 with a climate zone prescriptive solution. It specifies the minimum R value for the external insulation to avoid condensation. This value is also a function of the stud cavity R value, but Building Science Corp. typically recommends 1.5 inches of taped external foam.

What Ever Happened to Off-Peak Electric Rates?

In the 1970's, PSCO introduced off peak electric rates, which were designed to flatten their demand profile. At the time, a kwh used between 10pm and 6am was priced at less than a third of the cost of an on-peak kwh. If utilities can just tweak their customers usage habits thru rate schedules, they can really drop their capital costs. That is, they won't have to build that new power plant just to cover three week long spikes in demand.

Over the years, the PUC added many "cost adjustments" to the electric bill, which watered down the off-peak savings to be had. Eventually, all customers lost interest in the whole program and it was cancelled. These cost adjustments are multiplied by the kwh usage, and now account for around 66% of a residential electric bill. It didn't matter if all the usage was off-peak, these adjustments were still there in full. So, in 1980 if you were saving 2/3 of your bill with off-peak rates, by 2008, your savings would be 2/3 of the remaining 34%, or only 22%.

Finally a Foolproof Toilet Fill Valve to Save Water

We had three brand-new toilets that leaked slightly, apparently through the flapper. Even if it wasn't a significant amount of water, or caused a noticeable increase in the water bill, it caused an unsightly red mold to grow. Even though the toilets are cleaned weekly, the mold can be seen as vertical stripes in the bowl wherever the leak runs down the sides of the bowl.

Anyway, Fluidmaster now makes a new fill valve that refuses to refill if there is a slow leak. As soon as the handle is jiggled, however, it will refill. So a tenant can use it just fine with minimal inconvenience, but the normally wasted water is saved.

This may increase your callbacks in new single family construction, but it's the perfect solution for buildings with maintenance staff.

H4H Redefined the State of the Art for Zero Energy Homebuilding

With NREL, Habitat for Humanity has built and tested the simplest Zero Energy home that I've seen to date. Lots to learn from the following final technical report:

http://www.nrel.gov/docs/fy08osti/43188.pdf

Perhaps the most surprising lesson is the poor overall system efficiency of the solar thermal DHW preheat system. It shows that these systems may be hardly worth the effort. Ongoing maintenance for a system like this will further degrade the cost/benefit ratio for this subsystem.

NREL Denver Tour of Solar Homes

On Saturday, our East Wash Park home was on this year's Denver Tour of Solar Homes , sponsored by NREL.
Here's the blurb from the tour book:

Dickson Residence

This large house (4200 square feet) was completed in 2004 and is an updated version of the “Denver Square” design. The parcel was formerly a public service substation on three lots. The house uses a true direct gain passive solar design in that it has south facing glass and mass (concrete floors). Please note that the passive solar heating provides 90% of the space heating requirements – so much so that the radiant floor back up system is rarely used. If the owners were to do this again, they would install a less expensive backup system. In some places the concrete has been stained so that it is the actual floor. In other places, cork is laid over the concrete.

The house is joined to the building next door, which originally contained battery storage for the Denver Tramway system. Now the building houses an office and shop area.

The house is built using SIPs (structural insulated panels). In getting the permits for the house, the Denver plan review and inspection departments added eight months of delay in getting a building permit, according to the owner, because of their inexperience with SIPS. Greenprint Denver may be helping to alleviate the problems like this.

An interesting note is that three of the stained glass windows in the house were designed by a relative of Frank Lloyd Wright.

Passive Solar Features

Sunroom/mudroom

Mass of 2” of concrete on the floor

Trees planted on the east and west for shade control

Photovoltaic Panels

3.3 kW system

Grid tied

Utility bill has decreased $55 per month since installation

Thermal Envelope / Thermal Comfort

Insulated above code with SIPS

Low-e windows

Interior and exterior shades

Evaporative cooling (unique indoor cooler)

Expanding foam insulation around windows and outlets

Zoned heating

Night setback thermostats

Radiant floor backup heating system

Lighting

Some CFL lights

Motion sensors or timers in the mudroom and garage

Construction

6” thick SIPS walls

Thermal breaks at entry doors and perimeter of entire foundation

Pre-plumbed for solar thermal collectors

Lightweight Metal shingles

Appliances

Energy Star rated

Sealed combustion boiler/hot water heater

Transportation / Lifestyles

Hybrid SUV

50% of all errands are done by bicycle

Light rail is used once a week

Recycling

Composting

Vegetable gardening

Re-Use / Salvaged Materials / Recycle

Reclaimed brick

Reused existing building and converted into a home office from its original purpose

Unique Features

Homeowner trained in solar during the energy crisis of the 70’s

Homeowner holds patents for pneumatic fittings, valves, and a nose hair trimmer

Green Features

EPS insulation

Stained concrete floors

Reused an entire building and converted into a home office

No particle board was used

Steel roof

Cork floor

Water Features

Low flush toilets (5 out of 5)

Low flow shower heads (3 out of 3)

Xeriscaping

Drip irrigation

REC’s and Windsource

On demand hot water system: “Doorbells” in each bath summon hot water without wasting it

A little bit of nice publicity from the WPP....

http://kevintesting.googlegroups.com/web/WPPKTD.pdf?gda=0Va3kDwAAAAnKIMncx6ukRKQXuLFP__Do_CwWda2FNSImGT2MKwxy2HpCSjbUfPiF0VurU3U4gL9Wm-ajmzVoAFUlE7c_fAt