Tough Decision

Ryan and I are trying to figure out the water heating piece.

We know that we want solar. We have decided on a Drain-Back system for the initial water heating. The cost will be somewhere between $11- $13,000 to have Solar Energy Solutions install it.

We decided on this configuration for several reasons: it is the most maintainence free configuration, there will be no worries about anything boiling over or blowing a gasket in the summer, no glycol (at $50 a gallon this is a good thing) and there is some awesome monitoring that we will be able to set up.

That decided we now have the water heating piece.  The solar system deposits its pre-heated water into an 80 gallon tank. Fair enough. In the summer, this will be all we need. In the gloomy months however, we will need some kind of heater to heat the pre-heated water so that it is hot.

This is where it gets complicated.  Per the Energy Petal, all of our energy usage has to come from renewable resources.  NO!!! WOOD IS NOT CONSIDERED RENEWABLE|. Can you believe it??  I just learned today that there are NO COMBUSTIBLES ALLOWED in Living Building 2.0.    No wood stove. Can you imagine living in the woods and not being allowed to use a wood stove?  If they could burn wood 2,000 years ago, we should be able to burn it now as it is carbon neutral.  I digress.

Lucky for us we are in the Pilot Project so we can have some combustion. Baby steps. I for one don't think the technology is there yet to have no combustion, but that's just me.

We were researching electric water heaters and gas water heaters and learning a lot. Then Andrew of Solar Energy Solutions suggested that we use a tankless water heater. We have one at our house right now and to be honest, I have not been blown away by the energy savings, but mine was installed in 2003. I hear that they have gotten a lot better. Andrew suggested we look into a Takagi TK3 as it is the only truly solar compatible tankless water heater.  What does "solar compatible" mean?

Most tankless water heaters take the water, at whatever temperature it comes into the unit at, circulates it and causes it's temperature to rise a certain degree (say a rise of 60 degrees). So if your water is 40 degrees entering the unit, it will be 100 degrees when it comes out. There are some adjustments, but on the Bosch I have here, it is just a knob that you turn. Solar compatible units monitor the incoming temp of the water and only apply enough energy to heat it to a certain temperature, thereby using a LOT LESS ENERGY in the process.

The problem is that the Takagi uses natural gas or propane. Combustion is not allowed!!  To add another layer of complexity,  we are going to have a Hydronic Radiant Floor Heating System, which is a closed loop system, therefore needing it's own heater as well. We had thought that we would get an air to water heat pump to be used solely for the floor heat. Keep the systems separate...Simple enough right?  Wrong.

The heat pump is run on electricity which helps us with the renewables requirement but the one that we have been looking at, The Daikin Altherma, also has a domestic water piece. So, it can be the domestic water heater for those gloomy months. OH... it also has a solar preheat piece.  So now we have the possibility of having two separate systems that do exactly the same thing but in totally different ways. Can we have one system do everything?


We have a call into a friend who is using the Daikin in his house and this will hopefully give us some answers. Like... how exactly does one heater give both water for hydronics and domestic hot water?  Do we end up drinking water that has run through the tubing used to heat our house?  Will a tankless water heater fill the bill for the hydronic system (we wish that it was electric).  What is the actual cost?  The Takagi is less than $1000 and it seems like the Daikin is over $10,000. If this was only about the cost, I think it would be easy but then there is the efficiency factor.  Heat pumps are super efficient while the tankless water heater might be expensive to operate because we will be using Propane.

This video might help:

If anyone has a comment or opinion, we would love to hear from you.  :)

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