Suncroft House Virtual Tour
1. Introduction
2. Site
3. Site Challenges
4. House Design
5. Roof
6. Gutter
7. Downspout
8. Downspout Filter
9. Piping to Rainwater Tanks
10. Tank Enclosure
11. House Entry on First Level into “Family Room”
12. Half-Bathroom
13. Floor
14. Radiant Floor Heating
15. Floor Insulation
16. Wall Insulation
17. Laundry Room – Solar electric equipment
18. Critical Loads Panel
19. Laundry Equipment
20. Mechanical Space
21. Battery Bank
22. Ground-source heat pump (GSHP)
23. Radiant Heat Buffer Tank
24. Domestic Hot Water Tank
25. Solar Hot Water
26. Potable Rainwater System
27. Plumbing Manifold
28. Heat Recovery Ventilation (HRV)
29. Kitchen Appliances
30. Lighting
31. Daylighting
32. Windows
33. Passive Cooling
34. Outdoor Kitchen and Dining Room
35. Third Level
36. Electric Bills
37. “Passive House” Comparison
1. Introduction
Following the British tradition of naming houses, Suncroft House is based on the word “croft”, which is a small homestead.
2. Site
There are two adjoining lots, totaling 2/3 acre. A small creek runs through the lower lot. Plans for the site include permaculture food production, with raised beds and a forest garden.
3. Site Challenges
The house is situated on the north-facing slope of a hill, whereas the ideal would be a south-facing slope. As a result, the path of the sun is very low in the winter, and there is increased shading from trees and buildings. Another challenge was that the hillside slope is 45 degrees from the north-south axis. Instead of having the house aligned with the hillside contour, the roof faces directly south for better solar performance. As a result, the elevation changes appreciably from both “front to back” and “side to side”, and a more complicated house design was required. Another challenge was that the best views are in the northern direction. Instead of minimizing the window glazing on the north side of the house, we compromised our energy performance by having more windows here than we otherwise would have done.
4. House Design
The house is a tri-level design, with a half flight of stairs between levels. The area of each level is about 300 sf, for a total of 912 sf. Each level has an adjoining porch or deck, to expand the living space with semi-outdoor rooms that don't require energy for heating or cooling.
5. Roof
The roof is especially important, as it provides energy and water for the house. A larger roof provides more space for solar panels and more area for rainwater collection. During the design phase, the area of the roof was increased by extending it over the second and third level porches. The photovoltaic (PV) array has 36 panels, each 170 watts output, for a total rating of 6,120 watts. The PV panel mounts are raised about 8” for better airflow underneath resulting in lower temperatures and better efficiency in the summer. Special mounting devices (“S-5!” brand) were used to clamp the array to the standing seams of the metal roof, avoiding penetrations to the roof. The PV array was mounted as high as possible, with accommodation for cleaning access. The solar hot water panels are not so sensitive to partial shading and are mounted on the lower section of the roof. Since the roof is the collector for the household's potable water, special precautions were taken regarding roof materials. The roof surface is Zincalume/Galvalume, which came with an acrylic clearcoat. All flashings had to be lead-free. All caulking and sealant materials for the roof, gutters, and downspouts had to be approved for potable water contact.
6. Gutter
The gutter material is also Zincalume/Galvalume, in the large 6” size since there is a single gutter for the entire roof. The gutter was sloped more than usual, to give a higher water velocity (for a cleaner gutter), and to enable it to drain completely and dry out quicker. For rainwater harvesting purposes, a minimum slope of 1/16” per foot is recommended for gutters, and for Suncroft House a gutter slope of 1/8” per foot was used for even better performance.
7. Downspout
There is one downspout for the entire roof, and rainfall volume calculations showed that a 4” diameter was recommended. The downspout material is special 4” PVC piping approved for potable water (“pw” is marked along the pipe length). It was a big disappointment that a workable alternative to PVC was not available at the time.
8. Downspout Filter
A downspout filter is within easy reach of the second level porch. This strains debris from the rainwater down to about 1000 microns (as the openings in the filter screen are about 1 mm in size, and there are 1000 microns to a mm).
9. Piping to Rainwater Tanks
Within the bumpout along the outside of the second level porch railing, a 4” pipe carries the rainwater to the tank enclosure.
10. Tank Enclosure
The tank enclosure is integrated with the house design, under the third level porch. The tanks rest on a reinforced concrete slab. The two tanks are kept shaded to prevent the growth of algae and to avoid the ultraviolet degradation of the tank material. The enclosure also provides protection from freezing during the winter. The tanks are made of food-grade HDPE (high-density polyethylene), the same material used for milk jugs. Each 3,000-gallon tank is 8-feet tall with an 8.5-feet diameter, for a total capacity of 6,000 gallons. Rainwater is gravity-fed from the downspout to a roofwasher filter, which filters the water down to 60 microns before it goes into the tanks. (Recall that the water had previously been strained down to 1,000 microns.) This device also does a “first flush” of about 10 gallons, so that contaminants from the roof surface are diverted at the beginning of the rainfall. There is a tank bypass valve, which can direct the roof runoff to the stormwater drain when necessary (such as while working on the tanks or cleaning the roof). The tanks are connected together with flexible hoses, since rigid connections can leak from movements of the tank walls when the tanks expand and contract as the water level changes. The 2” ID food-grade hoses are the same type used in wineries and breweries. The tanks are connected so that the can be filled in parallel or in series, depending on valve positions. This gives flexibility in case one tank is out of service. Each tank has a 4” overflow pipe leading to the stormwater drain. There is water pipe leading to the tanks, so that the tanks can be manually filled with city water, if desired (such as for off-peak filling for summertime irrigation). The tanks have an outlet pipe that sends rainwater into the house for treatment before being used.
11. House Entry on First Level into “Family Room”
This room is used for watching videos, playing video games, and other activities. There is a woodstove (very high efficiency and very low emissions) here for emergency heating and cooking if the grid is down for an extended time in the winter. Otherwise, we don't use the woodstove at all since we're achieving net zero energy using electric heat only. The woodstove has never been used other than to test it during the summer before we moved into the house.
12. Half-Bathroom
Adjacent to the family room is a the half-bathroom with a dual-flush toilet. Button number 1 uses less than a gallon to flush, and button number 2 uses the standard low-flush 1.6 gallons. The sink has an aerator limiting the flow to 0.5 gallons/minute. This room has a frosted glass window for daylighting.
13. Floor
The floor on the first two levels is made of concrete, 3 inches thick, which was pigmented to the final color before it came here by truck and was poured. While the concrete was still soft, the workers hand-tooled some control joint grooves in a grid pattern that we specified. After the concrete cured, we put grout in the joints to make the floor resemble tiles. We finished the concrete surface with a water-based, low-VOC sealer.
14. Radiant Floor Heating
Embedded in the concrete is a back and forth pattern of PEX polyethylene tubing. Hot water is circulated through the tubing, warming the slab and heating the room. Each of the three levels of the house is a separate heating zone with its own thermostat (mounted at the standard 5' above the floor level). Radiant floor heating is a relatively comfortable way to heat a house. With radiant floor heating, the warmest part of a room is from the floor to the 5' level. (In contrast, with forced air heating the warmest part of a room is typically from the 5' level to the ceiling, due to the stratfication of the warmed air.)
15. Floor Insulation
The 3 inches of concrete were poured on top of 3 inches of rigid foam insulation. Below that is subflooring supported by 12” deep TJI joists spaced 2 feet apart. The 12” deep spaces between the joists are filled with spray foam insulation. The entire floor structure has a thickness of approximately 19 inches, of which about 15 inches consists of insulation.
16. Wall Insulation
The 8-inch exterior walls have staggered stud construction (with 2x4 studs installed every foot in a staggered pattern) to avoid “thermal bridging” heat losses across the wood structure. The exterior wall cavities are insulated with spray foam. Upon application, the foam expands to fill cracks and crevices, and blocks infiltration.
17. Laundry Room – Solar electric equipment
This is the location of our solar electric system inverters, etc. The system is grid-tied with battery backup. The PV panels on the roof are wired to produce 48 volts of DC current. The DC output is wired to the two charge controllers to keep the batteries topped up, before being sent to the two inverters, which covert the 48V DC current into 120V AC household current. If we are making more electricity than we're using at the time, the extra production is sent into the grid. The utility's meter outside shows two numbers: the energy sent into the grid, and the energy taken from the grid. Monthly meter readings are done by the electric company to determine whether we owe them money or if they owe us money. Over the year, if we produced as much or more than we used, then we achieved net zero energy. Actually, the house is doing much better than net zero energy, producing almost three times the amount of energy that it uses. We're like a local neighborhood power plant, sending renewable electricity into the grid for others to use.
18. Critical Loads Panel
Near the inverters is the “critical loads panel” which has circuit breakers for certain circuits that switch over to battery power during power outages. The refrigerator, ventilation, solar hot water system, and some lighting and household circuits remain powered during grid failures.
19. Laundry Equipment
We searched the the Energy Star website to find the best performing washing machine available at the time. It is a front-loader with a very high speed spin cycle, so the clothes will dry faster. We do not have a clothes dryer – they use so much energy, they don't qualify for Energy Star. We air dry all clothes, either outside on lines or inside our ventilated mechanical space on drying racks when the weather is unsuitable. One of us grew up in England, where four children were raised in cloth diapers without ever having a clothes dryer. And that's England, not Arizona. If it can be done there, it's possible here.
20. Mechanical Space
The mechanical space is like a well-insulated crawlspace, with headroom over 6' , insulated concrete slab floor, and forced ventilation (both fresh air and exhaust).
21. Battery Bank
The distance between the battery bank and the inverters is minimized to reduce the resistance losses of the DC current as it flows through the cables. The battery bank is modest sized, with 4 fairly large, sealed, maintenance-free deep-cycle batteries. They are mainly for powering the fridge, ventilation, solar hot water, and some lights during power outages. If the grid goes down, the battery bank should last for maybe 3 days, longer if it's sunny and able to recharge.
22. Ground-source heat pump (GSHP)
The GSHP is located indoors and it saves a lot of energy for us. This model does both the space heating and the domestic hot water (which is not common). A heat pump is similar to a refrigerator, but instead of taking heat out of the refrigerator and freezer compartments, it takes heat out of the ground. A 240-foot deep hole was drilled in the yard, and a piping loop was installed to pick up some heat from the Earth where temperatures are around 50-55 degrees a few feet below the surface. The length of the piping loop was determined by calculations based on the expected heating requirements of the house. The site conditions were unsuitable for making a long enough trench (4-6 feet deep), so we went vertical, using a well-drilling truck. The process is similar to drilling for a water well, except that casing pipe is not installed in the hole, and the hole is filled once the piping loop is put down there. Most heat pumps that are used locally, like the ones seen sitting outside houses, are “air-source” heat pumps. Ground-source heat pumps are more efficient since they are getting heat from the 50-degree ground, compared with getting it from below-freezing air. Air-source heat pumps typically require an electric resistance heating backup for when the outdoor temperature is below 20 degrees or so, which hurts their efficiency. For comparison purposes, if electric resistance heating is assigned an efficiency of 100%, then air-source heat pumps would have efficiencies in the 200% range, while ground-source heat pumps would have efficiencies in the 300% range. This particular unit has a Coefficient of Performance (COP) of 3.6, meaning it is 360% efficient when compared with electric resistance heating. In other words, electric baseboard heaters and the low temperature backup for air-source heat pumps use almost 4 times the energy for the same heating output as this GSHP. We could have had our GSHP configured to provide air conditioning during the summer months (it would chill the concrete slab instead of heating it), but we specifically ordered a unit that did not have this feature, since the house is designed for passive cooling (without additional energy inputs).
23. Radiant Heat Buffer Tank
This is a standard 50-gallon electric water heater with above-average insulation, but the electric power supply was never connected. During the heating season, the GSHP brings this tank temperature up to 90 degrees and shuts off. Each of the 3 levels of the house is a separate zone with its own thermostat. When a thermostat calls for more heat, a small pump circulates the warm water from this tank through the tubing in the floor. When the tank temperature drops to 80 degrees, the GSHP turns on and brings it back up to 90 degrees, then shuts off again.
24. Domestic Hot Water Tank
This is a 50-gallon electric water heater (identical to the radiant heat buffer tank), and its power supply is turned off at the circuit breakers. (The electric power supply is for backup purposes in case the GSHP is out of service, but we have never had to use it). The solar hot water tank output goes into this tank. If the solar hot water tank temperature needs boosting, then the GSHP heats it the rest of the way, before sending the hot water to the plumbing fixtures. An interesting sticker on the tank shows the Energy Guide Rating for normal use (without GSHP or solar hot water preheat): 4721 kWh is the expected energy use per year, for domestic hot water only. Compare this to the actual electricity used by the GSHP for both space heating and DHW combined: less than 1,050 kWh per year. (This reading comes from a separate meter we have hooked up to the GSHP to show its energy consumption.)
25. Solar Hot Water
This is a typical installation, with two panels on the roof (each 4' by 8'), and an 80 gallon tank (with built-in heat exchanger). In simplified terms, whenever the roof panel temperature is hotter than the tank water temperature, the system circulates a glycol-based antifreeze between the roof panels and the tank, transferring heat to the water in the tank. Sunny days in the winter will bring the temperature of these 80 gallons above 120 degrees. In the summertime, the 80 gallons are typically heated to above 150 degrees. There is a mixing valve that adds some cold water to the water coming out of the tank, if necessary, to bring its temperature down to 120 degrees. 80 gallons of 150 degree water can keep the family in hot water for a couple of cloudy days. For more than half the year, the solar tank provides all of our domestic hot water (there is no need for the GSHP to increase the water temperature, and the domestic hot water tank can be bypassed.)
26. Potable Rainwater System
Polyethylene PEX piping brings the rainwater from the storage tanks to the indoor pump. The pressurized water is forced through a series of three filters – from 60 micron in the tank the water is filtered down to 20 microns, then to 5 microns, then to either 1 or 2 microns (with activated carbon) – before being passed through ultraviolet light. The UV light effectively “disinfects” the water, so viruses and bacteria aren't a problem. Additional point-of-use filtration occurs at the kitchen and bathroom sink faucets, down to 0.5 micron. PEX piping brings the purified rainwater to a 3-way valve. This valve is for choosing either rainwater or city water to go to all the household's plumbing fixtures. Between the 3-way valve and the city water shutoff valve is a backflow prevention device, which eliminates the possibility of rainwater getting into the municipal water system piping. The purified rainwater test results show no contaminants (below measurable levels). The municipal water test results do show measurable levels of contaminants.
27. Plumbing Manifold
From the 3-way valve, the water is supplied to the plumbing manifold, where each plumbing fixture has its own shut-off valve and dedicated supply line, for easier servicing and operation without interference from other fixtures. Each PEX piping run (both hot and cold) are fully insulated – to save energy for the hot water pipes, and to reduce condensation for the cold water pipes.
28. Heat Recovery Ventilation (HRV)
With a very tight house and very low infiltration of air, mechanical ventilation is required. The HRV provides fresh air throughout the house, and exhausts air from the kitchen, bathrooms, laundry room, and mechanical space. Heat contained in the exhaust air is used to preheat the incoming fresh air. WITHOUT an HRV, the kitchen and bathroom fans would be blowing warm air out of the house. WITH an HRV, around 70% of the heat content of the exhaust air is recovered. This particular model uses only 17 watts on low speed. We normally run the HRV to ventilate the house 24/7 on cycles of 20 minutes on, 40 minutes off, on low speed, with booster switches (in bathrooms, kitchen, and laundry) bringing it up to a continuous high speed. During days when windows are open, the HRV is only used in the booster mode. When used on hot summer days, after the house cools down overnight, the house windows are closed and the HRV precools the incoming fresh air with the exhaust air.
29. Kitchen Appliances
All appliances, including the telephone answering machine, were chosen based on Energy Star ratings. The refrigerator is a Kenmore from the local Sears, instead of the more expensive Sunfrost brand. This Sears model uses 15% more energy, but it has 25% more capacity than the Sunfrost. It also costs over $2,000 less than the Sunfrost. We have no electric dishwasher, so all our dishes are done by hand. We could add a dishwasher later, but we have a vegetarian kitchen with no grease that needs really hot water, and we plan to save dishwater for watering outdoor plants. We have no full-sized range installed. Instead, for baking we use a large convection toaster oven (large enough to bake two 12” pizzas at one time), and a large convection microwave. Instead of a permanently installed stovetop, we maximize our available counter space by using portable induction cooktops. Induction stoves and cooktops have the highest efficiencies. A gas stove loses 40% of its heat to the surrounding air and metal, so it is 60% efficient. A normal electric stove is approximately 75% efficient. An induction stove is about 90% efficient, since is heats only the pan (the cooktop surface is not heated). Induction cooktops built into the counter can be pretty expensive; we use a couple portable offbrand units that we found on sale for around $100 each. The microwave oven is plugged into an outlet with a wall switch to avoid phantom loads. A Kill-A-Watt meter showed that it uses 8 watts just from being plugged in, so we turn off the wall switch between uses (more convenient than pulling out the plug each time, and easier on the cord).
30. Lighting
All lighting in the house, if not daylight, is either CFL, fluorescent, or LED. The hanging lights in the kitchen and dining areas have dimmable CFL bulbs. Dimmer switches can result in increased bulb life – dimmed to 90% of output, a dimmable bulb supposedly lasts twice as long. Above the kitchen sink are 4 fixtures each with a tiny 2-watt CFL bulb. In addition to the regular lighting, each room has a 12-volt DC light fixture that feeds directly off the battery bank, for better efficiency during power outages. Some of these DC fixtures have 5-watt DC CFL bulbs, and some have quarter-watt DC LED bulbs (only 0.25 watts) – these draw so little electricity that they can probably be used indefinitely during power outages.
31. Daylighting
Most of the walls in the house are painted a slightly lemon-white tint for better daylighting than deeper colors. Both bathrooms have frosted glass windows for daylighting, which gives light to the bathrooms at night when other room lights are on, so it's not always necessary to turn on the bathroom lights. The upstairs bathroom also has a well-insulated “Solatube” light fixture that eliminates the need for turning on the lights during the day.
32. Windows
All the windows have fiberglass frames, which have better thermal properties than vinyl or wood. They have low-e coatings and argon-filled panes for lower heat losses. All the windows are either casement or awning windows which clamp shut against their seals, typically resulting in less infiltration than other types of windows. Casement windows also open all the way, giving better ventilation and better cooling during summer nights. Other window styles, like double hung or sliding windows, only open halfway. Roof overhangs on the south side of the house were calculated to shade the windows on summer days, while allowing full sun during winter days when the sun is low in the sky.
33. Passive Cooling
Instead of air conditioning, the house is designed for passive cooling without any additional energy input. During the hottest days in the summer, when it reaches 96 degrees in the shade, the highest indoor temperatures are only 71 degrees at the front entry level, and 74 degrees at the two upper levels. This is lower than many people set their air conditioning. This passive cooling is achieved through a combination of: a superinsulated, tight building envelope; a strategic placement of windows to minimize summertime solar gain and to maximize ventilation at nighttime for “night cooling”; high thermal mass inside to cool down at night and stay cool throughout the day; windows closed (and some shaded) when outdoor temperature exceeds indoor temperature; HRV used during hot days to pre-cool incoming fresh air with exhaust air; and using our outdoor kitchen space on the back deck to keep the cooking heat out of the house.
34. Outdoor Kitchen and Dining Room
The second-level porch, located just outside the kitchen door on the eastern side of the house, is our outdoor kitchen and dining room during the summer months. There is counter space for cooking with the toaster oven, microwave, and portable induction stoves, which keeps the heat out of the house. There is also space for seating 12 people for a meal.
35. Third Level
The third level of the house consists of two bedrooms and a full bathroom. The stairs and all of the flooring are made of bamboo, except for the linoleum flooring in the bathroom. The radiant floor heat tubing is attached under the subflooring, using special metal plates to increase the heat transfer. A thermal feature of the bathroom is that the ceiling, floor, and all of the walls are adjacent to conditioned space; in other words, none of these surfaces gets cold, increasing the comfort of the room's occupants. The heating of the bathroom is enhanced by a British “towel warmer” that is connected to the radiant floor tubing of the second level (kitchen/dining) zone. This acts like a mini-radiator, providing extra heat to the bathroom even at times when the third level thermostat setting turns off the floor heat.
36. Electric Bills
Since we produce more energy than we use each year, the electric company ends up paying us (though it amounts to hundreds, not thousands, of dollars each year). Most months of the year (including February some years) we do better than net zero energy. Since we produce so much more electricity in the summertime than we use, over the entire year the house produces almost three times the energy it consumes (without any burning of any kind). If we had no PV system on the roof, our biggest electricity bill during the winter would be only around $30.
37. “Passive House” Comparison
The insulation of Suncroft House is not thick enough for it to qualify as a “Passive House”, but its actual energy consumption performance is well within Passive House standards, due in part to all of its efficiency measures and the performance of the ground-source heat pump (compared to the electric resistance heating typically used in Passive Houses).
