Background
The genesis of the Wagner solar home was an unsuccessful search in the spring of 1980 for an existing house in Palo Alto. The Wagners, professionals with two small children, needed a house that had quarters for live-in help or that could be modified to provide such quarters. Ultimately they purchased in June, 1980 a small lot (6500 sq. ft.) on Chimalus Drive in Palo Alto. After intensive work over the next three months, they and their architect had designed an active and passive solar house for this lot, working with solar constraints that included several large trees and the rather large shadow cast on the lot from the garage on the property to the south/southwest.
In late August, 1980 the Wagners learned that the owner of the house to the south intended to add a second story to his house that would block almost all the sunlight from both the active and passive systems. They tried to purchase a solar easement as well as offered the free services of their architect to design the proposed addition. Their efforts however were unsuccessful. Their dilemma of whether to redesign and eliminate the solar features of the house or to seek another site was resolved when a larger site in the same neighborhood became available in September, 1980. The Wagners then sold the Chimalus lot, purchased the new lot, and began modifying their Chimalus solar passive design for the larger lot.
Design Requirements
The Wagners' design requirements for the house were the following:
• "Traditional" architectural style (i.e., the house couldn't look like most of the counter culture solar passive houses at that time)
• At least one very large room for entertaining
• Combined kitchen-family room
• Formal dining room
• Three bedrooms
• Den or guest bedroom
• Living quarters for live-in help with separate entrance
• Appropriate for raising a family with two kids
The design that evolved was a compromise among the design requirements, the site (a large flat, triangular site with tall eucalyptus trees partially shading all but the northern corner during the winter), cost-effective solar features, the limited budget of the Wagners, design features dictated by the earthquake code and structural engineering requirements, aesthetics, and spatial needs.
Design Features
The Wagner passive solar house is a two story slab-on-grade house with a pier and grade beam foundation and integral slab. The major living spaces face south with secondary spaces such as kitchens, bathrooms and the garage on the northerly exposures (the garage acts as a thermal buffer for the house and the kitchen generates its own heat through appliance energy losses). The five-sided plan maximizes the area of southern facades while minimizing the size of the north-facing walls.
The house is a direct gain solar passive design with 596 sq. ft. of S, SE, and SW glass (94 sq. ft. of NW and NE glass). Clerestory windows allow solar radiation to penetrate deep into the SE, S, SW oriented living room. All glazing is double glazed except for four large patio doors which contain Southwall Corporation's "Heat Mirror" glazing (R value of 4.5 vs and R value of 2 for traditional double glazed windows). Sliding glass patio doors are used extensively since they were the cheapest form of solar glazing. A five-inch concrete slab floor provides the primary thermal mass. I later installed 1000 sq. ft of unglazed French, dark, multi-colored quarry tile as the finished flooring throughout most of the ground floor which enhanced the thermal mass qualities of the concrete floor. A low masonry wall was designed to double as a linear seating area directly behind the southern glazing and as a modified Trombe wall to provide thermal mass but so as not to obstruct views from adjacent living spaces. Two SE and SW sunspaces (greenhouses) are attached to the house with sliding glass doors to allow natural convection of excess heat into the house living spaces.
The floor plan is an "open" design, which promotes natural convection of the collected solar heat. The northerly 6 inch walls contain R-19 insulation; the ceiling contains R-30 insulation throughout. The building code backup heating system employs radiant electric ceiling sheetrock panels (Panelectric by Goldbond). However, a zero clearance fireplace and super efficient Jodul wood burning stove provide all supplemental backup heating. The house is rough plumbed for a future active solar domestic hot water system, the solar panels of which will be located on the south facing roof with a tilt of 30 degrees. The other SE and SW facing roofs were designed for a future PV system.
The solar cooling features employ fixed overhangs to shade all south facing grazing, a solar chimney, and destratification fans. The fixed overhangs were designed to shade entirely the south facing glazing at solar noon on July 21 st and to provide no shading at solar noon on December 21 st . The internal space within the overhang roof framing is utilized for either storage space or for potted plants in the living room. The living room is open all the way up to a cupola (30 feet above the slab) which provides direct solar radiation during the winter through glazing on one side and solar stack-effect natural ventilation during the summer through fixed louvers on the other four sides (with insulating panels to prevent heat loss during the winter). Two destratification fans are provided: a "casablanca fan" in the high southwesterly facing master bedroom ceiling and a duct fan whose inlet is located high in the cupola and whose outlet is in the northwesterly facing den.
Performance
I used Berkeley Solar Group's "CALPAS" computer model (predecessor to one of the models authorized by the CEC for Title 24 submittals) to simulate the performance of the house on an hourly basis. This was the first detailed computer model available for modeling solar passive house features and since I was using the beta version of the model, I found an error in the sunspace subroutine which they subsequently corrected. Basically, this model used typical weather data and the physical characteristics of the house to predict various temperatures and backup energy demands. This model was used to make a number of cost effective decisions during the design process. These decisions included: deleting the modified Trombe seating wall as it produced very little stored energy; reducing the thickness of the concrete slab from 8" to 5" as the additional 3" provided very little additional energy storage; eliminating rigid insulation under the slab even though this was conventional wisdom at the time. The model predicted that the backup heating demand for a typical winter heating season would be about 35 million BTU. The total heating demand for the house during the first winter was estimated to be 110 million BTU as noted on the Title 24, Form 2 submittal. Thus, solar was predicted to provide about 75 million BTU of heating demand or about 68% of the total annual heating demand for a typical winter season.
The Wagners moved into the house in August, 1982 and have lived in the house since then. During the summers, the cooling features work very well and keep the house from overheating except during extended hot spells. Although the house is a solar passive house, the house requires the active participation of the residents. During the summer, the house is kept closed up during the day. When the outside evening temperature becomes cooler than the inside temperature, the sliding glass doors are opened and the destratification fans are turned on, and the thermal chimney cools the whole house to ambient outside temperature within one hour. The doors are left open all night and closed in the morning when we awake. During a typical summer day, the house temperature varies from a night low typically in the low 60's (or whatever the night-time low was) to a high in the low 80's. During a typical winter sunny day, the temperature varies from the mid 70's during the day to the mid 60's at night. On cloudy days and cold winter nights, the wood stove is run to maintain a minimum, comfortable house temperature. During the January 2007 record breaking extended cold spell, one night I neglected to fire up the wood stove. Upon awaking, the house temperature was in the high 50's. However with the sun shining from early morning and passively heating the house, by mid afternoon, the temperature was in the low 70's throughout the whole house. Surprisingly, there is little thermal stratification in the house, which indicates that most of the solar energy is going into heating the various thermal masses (concrete floor and sheetrock walls) and not into overheating the air.
When the house was built, numerous thermocouples were installed at different locations to enable monitoring of the performance of the house. Unfortunately, the monitoring equipment was never installed, so no hard performance data is available. However, based on the first winter's utility bills, a crude analysis of the backup heating demand was made. Assuming a non-backup heating electrical demand of 4 kwh/hr from 6-11 p.m. for weekdays (no one is home during the day) and 1.5 kwh/hr from 7 a.m. to 6 p.m. for weekends (plus the same nightly assumption as weekdays), the backup heating demand for October 1982 to March 1983 was about 11,200 kWh or 48 million BTU. This compares favorably with the CALPAS prediction given the following: Palo Alto experienced the wettest 1982-1983 winter of the decade; some parts of the house were unfinished, thus increasing infiltration losses; a relative visited for a month over the holidays and was using the backup heating system during the weekdays; the eucalyptus trees on the south property line had not been topped or removed; and a door between the house and garage was usually left open to allow a small dog access to the garage, thus increasing heat losses to the garage (a cat door was subsequently installed).
Green Building and Green Life Style Improvements
After living in the house for many years, we have made the following improvements to the energy efficiency of the house:
• Replaced most of the incandescent light bulbs with compact fluorescent lights (CFLs)
• Replaced the electric water heater with a gas water heater, thus taking advantage of the lower gas rates for the lifeline gas usage
• Stopped using our garbage disposal and started composting all our wet garbage
• Installed dimmers on all the lights
• Replaced appliances with Energy Star appliances
• Installed 800 sq. ft of raised beds to grow organic vegetables along with several organic fruit trees
• Collect compostable green and brown material from my neighbors and local tree pruners and prepare all my garden compost using a cold composting method
• Collect hardwood tree prunings from local tree pruners and split all my own firewood to supply about two chords of firewood per winter
• Recycle everything except ½ can of garbage
Future Green Building Plans:
I have plans within the next year to implement the following projects:
• Solar Photovoltaics: I acquired enough BPSolar Apollo thin film modules for a 2.5kw installation on the south and southwest roof areas of my solar house. I'm in the process of designing the system, applying for a rebate from the City of Palo Alto, and arranging to reroof before I can begin installation. I also need to negotiate with my neighbor to the south an acceptable plan to deal with the shading from eucalyptus trees on her property.
• Solar Hot Water: I acquired 3 used high quality solar hot water panels through the Palo Alto free yahoo group. I'm in the process of testing the panels for integrity and remaining life and designing a system for installation on my south facing roof that was rough-plumbed for active solar when we initially built our solar passive house.
