Solar Hot Water … Don’t Make a Bomb!

I’ve done a lot of reading lately as I layout the plumbing for our home.

The funniest statement I read became the title of this post … let’s try not to kill ourselves while building our dream home!

Before I dive into the solar heated water I want to back up a bit … what I have been doing over the last few weeks is try to come up with a plumbing plan for this building.  This has proved far more complicated than I anticipated; I don’t have extensive experience in plumbing, and many of the systems going into this house are not typical.  Regardless, stuff happens and apparently it also flows down hill … how hard can it be?

The plumbing for this project includes:

  • Domestic water supply,
  • Grey water planters,
  • Septic system and associated plumbing,
  • Solar hot water heating,
  • Radiant floor heat

Domestic water supply

The domestic water supply for our house includes the following fixtures:

  1. kitchen (sink, dishwasher although we may not install one, we wanted to have the hook-ups)
  2. main bathroom (tub, sink, washing machine, toilet)
  3. ensuite bathroom (shower, sink, toilet)
  4. Hot Water (tank?)
Other than identifying the fixtures listed above I have not done a lot of thinking about the water supply yet …
A 1″ line enters our house at the back of the utility U and will probably run underground to the main bathroom before being distributed to the various fixtures listed above.

Grey water Planters

Here again not a lot of thought has gone into the final design of the planters.

We have chosen to set the highest point of the planters at the east edge of the building and slope them down to the west edge of the building.  This means the flow of grey water is set and we need to get all of the grey water from the plumbing fixtures to the east-most planter.  To accommodate this layout our bathrooms will probably be a step-up from the rest of the floor plan … this will (hopefully) give us the height we need to get the grey water to the east edge of the building.

The other choice was to set the lowest planter in the middle of the building and have the grey water run to this point from two directions … this seemed more complicated and frankly we did not plan for this early enough … the benefit of this layout would have been smaller elevation changes due to shorter travel distances (possibly no step-up into the bathrooms).

Septic System and Associated Plumbing

This is actually where I started thinking about the plumbing … unlike everything else in this building a septic system has well defined code requirements and is fairly straight forward to implement.

The waste pipe layout is complicated by the need to separate out the grey water flow from the flow from the black water fixtures and run it to the grey water planters.  In our layout the grey water flow will be valved; it will either flow to the grey water planters or out to the septic tank.  This means that we are compliant with the building code, and did not have to try and prove that we did not need a code compliant septic system for this building.  We had an existing septic tank and field on our site and to get a permit we just had to have a certified septic installer o.k. our system.

Solar Hot Water Heating

There are a lot of options to consider when using solar heat, and everybody seems to be pushing their design as the greatest thing since sliced bread.  Added to this, the BC Building code (I believe this is similar across Canada) places restrictions on what you can use … all of this makes specifying a system challenging.

For a good introduction on different solar options this article helped me.

I found the following questions (taken from the website that warns against making a solar bomb) to be helpful …

The Fundamental Questions

  • Does the proposed system operate at low temperatures? Solar collectors are not very efficient at temperatures of 180°F.
  • Has the need for storage of solar energy been considered?
  • How will excess heat be handled?
  • How will the need for freeze protection be handled?
  • What will happen if the electric power fails in the middle of the day?
  • What will happen when the power comes back on after a period of stagnation?
  • If something goes wrong, will the system fail to a safe condition
    (fail safe)?
  • How will the occupant know if the system is not working properly?

Keeping these questions in mind the first system that occurred to me was an open-loop system that relied on a thermosiphon to pump the water around.  Confused yet?  This compares to a closed-loop system with glycol (antifreeze) and an electrical pump.  Read on … it gets worse!

We have already identified the need to block at least the lower half of our bathroom windows … its a privacy thing.  It occurs to me that this window space could be ideal for solar collectors … I even picked out evacuated tube solar collectors … these babies would obscure the view without completely blocking the sunlight … sort of like frosted glass … only functional!

By placing these tubes inside the building envelope (using the window glass as a cover) we could eliminate the need for a closed glycol loop.  In fact, the system could be an open loop thermosiphon … eliminating glycol, a heat exchanger and the need for a pump … talk about elegant.  What is holding me back from embracing this design whole-heartedly is two considerations:
  1. Will the lines close to the glass risk freezing at night, or if the building is un-occupied for an extended period of time?  Our building interior has not dropped below freezing in the two years it has been standing, but we have seen frost build up on the windows … a pipe close to the windows may risk freezing.
  2. Will the system generate a lot of undesirable waste heat in the building envelope during the summer months?

I am still tossing this idea around … variations on it are used in warmer climates.

With those considerations in mind the system that is currently winning is shown in the following image.

The solar panels are on the roof so it is a close-looped system and would use an anti-freeze solution in the heat exchange loop.  The necessity for an electric pump is eliminated by using a bubble pump … a solar pump that pumps when the sun is out by establishing a thermosiphon loop.  This pump is passive in that it works when the collectors are heated by the sun and shuts down when the sun is gone … which is pretty much when you want to pump … eliminating the need for an electric pump and a controller.

The hot water tank is used for storing the solar heat.  The tank could have an electric backup element or be propane … meaning that you will always have hot water … I still have not figured out which is the better option.

Radiant Floor Heat

We plan to have radiant floor heat in the high-use floor spaces of the earthship.  My intention is to use the solar heated water for the heating loops.

I am still trying to work this out but will look something like:

This means that the hydronic heating loops will not be passive, an electric pump will be used to move the water.  I have read about using a thermosiphon loop for this, but they still had a backup pump in case bubbles blocked the thermosiphon … so I do not think making this an active loop is a bad idea.  Our intention is to use a wood gasifier to produce electricity … the gasifier will also generate a lot of heat and I see it being primarily responsible for providing heat for the radiant floor system.  I have not shown it in this diagram because I am still wrapping my head around how it will be implemented.

Still a lot more to figure out here but this is a start.

I am curious what other people have done or come up with …

I will try to keep posting my design as it evolves … I am currently overwhelmed by the slope of this task and writing about it helps to clarify my thoughts.

Greywater, Plumbing and Helpful Resources

I’ve been designing the plumbing and grey water for our earthship over the last week … so I have been doing a lot of reading.

A few things have caught my attention during this process.

First, more recently written books in this space (green building, grey water design) are much more detailed than a couple of years ago.  When I first started investigating our house project I was able to find maddeningly little detailed information or knowledge about what we were undertaking … its one of the reasons we started blogging.

I am happy to say that this seems to be changing.  I have started reading Green from the Ground Up By David Johnston and Scott Gibson.    This book does not delve deeply into any one topic but it does a good job of designing ‘green’ from the start and making sustainable design decisions through the course of the entire project.  I have only read parts of the book that are relevant to what I am doing right now but I am pleased with my purchase so far … it is reminding me of issues that need to be addressed!

Even more impressive is a plumbing primer provided by the city of Winnipeg for home owners about to embark on a project involving plumbing.  More impressive because it is free and it does a good job of reducing complex code requirements to useful rules of thumb.  Plumbing code specifications will vary depending on your jurisdiction  but this is an excellent 101 class on plumbing … and did I mention it is free!

Does anybody have a reference they have been impressed with?   I am always looking for better information.

Back to slogging through Part 7 of the BC Building Code …

Laying Out Grey Water Planters and Plumbing for the Earthship

This last week has been challenging; we have been laying out the grey water planters and the bathroom walls along the south face of the earthship.

The challenge has been laying out the planters and walls while making sure we still have space for kitchen counters, walkways between the rooms and everything that has got to go into the bathrooms.  This process has involved a lot of discussion and some arguments.  Sandra and I are both still alive so I guess the arguments were not too bad.


Before laying out the planters we needed to establish a direction of water flow and planter elevation.  I did not give a lot of thought to the flow of grey water through the planters when drawing the plans.  I did locate the bathrooms along the south face as I felt this would simplify the grey water layout and I think that was a good decision.  Our earthship has two bathrooms though, and this  means we considered two options for water flow; a split system terminating in the same planter, and a shared linear system.  In the split system the kitchen and common bathroom grey water would flow through two shared planters and the bathroom off the master bedroom would flow through its own planter before ending in the same planter as the kitchen and shared bathroom.  The split system was my early favourite as it meant short runs from the grey water sources into the planters.  I was quickly overwhelmed by the complexity of laying out this system.  Not having planned for this idea from the start it was hard to fit our planter layout into a split system.  We settled on a linear system that starts at the east and of the building and flows to the west end.  This system means some longer runs than I had hoped for, but it is fairly easy to understand and design.

The other consideration in laying out the planters was elevation; both with respect to all the other planters in the system, and in relation to the grey water appliances that are feeding the planters.  The appliances feeding the grey water system (sinks, tubs, …) must be elevated above the planters (you need about 1/4″ of elevation per 1′ of horizontal travel of the grey water pipes).  In our case it means one to two steps going up into the shared bathroom so that we get sufficient elevation to get the tub water to the start of the planters.  Also, each succeeding planter in the system must be slightly lower than the one before it so that water flows through the system (like an underground river instead of a stagnant pond).  Again, we sloped the bottoms of the planters approximately 1/4″ per horizontal foot of travel.

The planters are linked together with pipes located about six inches off of the ‘floor’ of each planter.  This means that the 1st planter is connected to the second planter by a 2″ diameter sewage pipe.  The pipe leaves the first planter with the bottom of the pipe about 6″ off the floor of that planter and enters the 2nd planter again with its bottom about 6″ off of the floor.  This means that the pipe also slopes 1/4″ per foot of horizontal travel to encourage the flow of grey water between the planters.  The pipes are located close to the planter bottoms so that the grey water elevation is constant in the system … no one planter is a swamp or dry.

We ran these connector pipes a year ago when we did the initial excavation of our planter space.  We used our backhoe to dig a trench along the front of the building.  We did not give a lot of thought to the size or elevation of our planters at that time … we just did not want to be hand digging the planters a year later.  Our ground is clay and rocks … making it pretty tough digging!

Because we did not set elevations or think through the size of the planters last year we have spent a lot of this week DIGGING BY HAND (I am very glad James is here).   We had to re-grade the planter ‘floors’ so that they all consistently slope a 1/4″ per foot, and we had to dig up all of the pipes and set them properly as well.  Most of this work is done now except for the last planter on the west side of the building.

We have also started forming the walls of the planters.  Again, the work we did a year ago digging the planters was not very accurate.  Most of our initial holes were wider than the intended planters.  This means that we have been forming pop can/concrete walls from the bottom of the planters up to our desired planter wall height.  Ideally, we would have been able to start the walls on the outside perimeters of the initial excavations, reducing the work and materials required.

Underneath the pop can walls that form bathroom walls we placed a small concrete footing (6″x6″).  Underneath the pop can walls that form planter walls we excavated a small trough and filled the trough with concrete before laying cans.  The footings contain engineered fibres and is a standard mix (1 part cement ; 2 parts sand ; 3 parts gravel).  None of these walls are load bearing; the purpose of the footing is to create a flat, level working surface for the walls.

All in all it has been a productive week!