Prefab Green Home Systems Post #2: The Heat For Our Net Zero Energy SIPs House Kit
We have certainly been thinking about heat for our prefab net zero off grid house this week.
We had one of the biggest snowstorms in recent memory begin Friday, and on Sunday we drove slowly, carefully to vacation in West Virginia.
So where to vacation? The Greenbrier.
Experiencing what still works in a resort founded in 1778 allowed us to observe and apply timeless elements to our own modern prefab net zero house, today. We have the prefab advantage of highly energy efficient structural insulated panels, passive solar design, radiant heat in the polished concrete floors. What resonated with me was the importance of cozy cottage comfort after a brisk hike in the crystalline air; wet freezing children shedding thick layers of soppy, stiff, half-frozen crunchy clothes...
As you drive through the mountains today, you are aware of how dangerous weather can be - and imagine the perilous journeys over centuries, even just decades ago with no shelter, no dry welcoming warmth, no means of communicating for help.
Still in this day and age, the roads can be treacherous.
We took our time.
My northern German husband who went to graduate school an hour away from the Alps was surprised and intimidated by the road conditions we encountered.
Finally, we arrived...
We knew we had a cottage... but didn't expect... THE Cottage.
What we took back with us, after a glorious few days sledding and hiking in the elements yet always within reach of immediate creature comforts was... the admittance that in rural areas, despite the coolio latest technology that allows passive solar, net zero comfort... you need to also always think about the dire situations...
Y'know, Dire Straits...
Not in a fear-mongering way. In a practical, affordable, positive way, as a boost to our otherwise comfortable solar systems, our prefab's passive solar design and energy efficient, tight insulation; to ensure that we're also really ready for rugged, rural, sometimes desolate and emergency conditions.
On cue, as I continued my ongoing reading journey of The Moomins with my children tonight, Snufkin ran up into a similar scenario with no less than twenty four little woodies he had somehow acquired after his revenge on The Park Keeper. Tired, cold, wet, hungry, they arrived at a cottage. Inside: a wood stove, and a pot of beans. Soon their wet cold clothes were hung, empty bellies filled, and...
Hurrah, they were saved.
And this is what I think:
Honeychile, there's never harm in good back up. In fact, you rely upon it.
* Fer you astute history and enviro business buffs, the whole Coal Country experience is something to be addressed in a separate post, in itself a whole different experience... wow. More soon, in a whole different post focusing on economy and scale of local industry... industries.
Here is... The Heating Post.
(Schematics later, here begins Handsome Husband's thoughts:)
Space Heating and Domestic Hot Water (DHW) For The off-grid zero energy prefab home:
We have been planning and realizing our prefab off grid net zero SIPs house for 3 years now. The actual construction began a year ago. Although the prefab house kit was erected and sealed in with windows, doors, etc. within a week, one of the factors leading to our own extremely long period of construction once the exterior was weather-tight was the search for a solution to our heating needs that fits our building structure, geography and long-term goals. (House kit consumers could certainly have finished the interior long before we have with our own prefab house kit!)
To better understand the amount of choices let’s compare the issue to off-grid power: You can calculate how much power you need (or want), how many days of power supply you want to be able to store in your battery bank and whether you want back up power. All that is left then is choosing from solar, wind or water as your primary power source – a fairly well understood calculation.
For hot water and space heating the options are far greater:
We can collect heat from the sun via solar hot water collectors (flat plate or evacuated tube designs) or take advantage of the warmer temperature in the ground below our dwellings (geothermal heat).
We can store the collected heat in tanks filled with liquids or bunkers filled with sand. Either needs to be insulated to preserve the heat until we need it.
We can heat our spaces by transferring the stored heat to warm air or warm liquid.
Backup really refers to the conventional heating system and obviously should be used as little as possible. This presents the biggest challenge as we want to avoid it at all means but still have to account for it.
The solution you select depends on your goals:
We need to protect our homes from catastrophic failure.
We need to determine what level of comfort we expect if freeze protection is covered. This is a personal choice. One may state “I am fine with not taking hot showers” or “I will put on a sweater or two” if my heat storage is depleted or one may say “I want to have a choice to take a hot shower or maintain a warm temperature”.
In our case we want to be able to make the choice. This allows us to ask of the design to provide us with comfort when the system is depleted.
During a birthday party for one of our son’s classmates I spoke to the father about the casa ti. He installs heating systems for a living. I shared our observation that the passive solar architecture in conjunction with the highly insulated building envelope due to the Structural insulated Panels (SIP) is not losing a lot of heat at night. On a sunny day leading up to a night around freezing the house looses 4-5 degrees until the next morning. His comment was “your heating system won’t have to work very hard”.
This is critical for our project since a highly efficient and well insulated building simply won’t require much heat. We have proven during our open house in September 2009 at our Prefab Green Open House that you can heat the building solely by inviting 30-40 people (in this case some of you reading this) and the heat radiation from their bodies will heat a space. Arrivals during the open house instinctively took off their coats on what was a rainy, cold day.
So here is how we are going to heat our prefab net zero green home, the casa ti:
We are starting off with 30 evacuated tube collectors by Apricus.
We are using 2 80 gallon conventional water heaters from our local building supply that we daisy-chain into a 160 gallon heat store. We will choose tanks/heaters with high insulation and will wrap them in additional insulation. The burners won’t be used at all (see backup below) so we can wrap them as we wish.
We are using radiant heat. The foundation of our prefab house kit casa ti has 6 loops of PEX tubing, each less than 250 feet of length which is important to deliver heat evenly. 3 loops each are assigned to zones (North and South). The concrete slab rests on 2” of rigid foam insulation where the slab doesn’t support load bearing walls (perimeter and central East/West wall) and the foundation has 2 feet vertical and 2 feet outward insulation.
An on demand water heater powered by LP gas is spliced into the heat supply to the loops.
Backup While We Are At The Prefab House
A recycled wood stove (the stove Copeland's own family used in the 1980s) supplies heat to the dwelling while we are present. The required heat recovery air exchanger will help distributing this isolated heat source to the entire house as it extracts air (and heat with it) from designated areas of the house and delivers fresh air alongside with the heat extracted from the discarded air to the bed rooms.
In the meantime... stay warm...
'Cause baby, it's cold outside...
P.s. If you like pictures (you may have noticed I do), here's more pictures of The Greenbrier, the cottages there, and the drive. : )
A hike, and sledding:
One last morning sledding, then we headed home: