Unpressurized Heating Systems

Since we make unpressurized tanks, I like to play with the water in the tanks. Our tanks started out life as storage for solar drainback heating systems. They are simple and work well.

It seemed to be logical to use that same water that is in the tank for heating things directly. You can pump the water out of one of our tanks into a hot water baseboard or a radiant floor and not use a heat exchanger. If all the materials in the system are non-ferrous, there is no treatment required for the water. Of course, you do need to use a bronze or stainless steel pump.

I have such a system in my home. There is a 350g Heat Bank in the basement and we pump out of the tank with a Taco 007 bronze pump to the five zones of radiant heat in the house. I was a little concerned that the 007 might not make it to the second floor, but it did and everything works fine. To keep noise down, the return line to the tank should always be submerged into the water, but other than that, it is pretty simple.

That same tank water also circulates to a small stainless steel boiler that we have been developing.

The beauty of these simple systems is that they only require a pump and do not use a heat exchanger. Now, I am very happy to manufacture and sell heat exchangers. Our heat exchangers are very efficient and are not horribly expensive. However, they are an additional cost and in an unpressurized system, they are not always necessary.

I have done these systems over the past 25-30 years and have always been pleased with the results. They are not for every home. If you think you might be a candidate, give us a call, we can help you sort through the issues.

We do have a backup system in place. We had originally used a Toyotomi OM-148 oil-fired water heater for space heat and domestic hot water. It now functions as a backup to our wood system. I turn it on manually since it does use oil while on standby and I hate using oil.

Pressurized heating systems do have their place. So do unpressurized ones.

Sometimes, different is good.

Have a Happy, Healthy and Prosperous New Year!

Tanks and Insulation

I got a call Friday from a solar contractor who had a request for a quote on a solar heating system with a 1,000 gallon tank that is insulated to R-78. I reminded him that our tanks are insulated to about R-32 but knew the product the RFP was referring to. (Sometimes architects and engineers base their specifications on a favored company’s product so the bid process favors that product.) Being a good entrepreneur, I also offered to quote him on a 1,000 gallon R-78 tank.

This started a whole thought process on what is the best insulation value for a heat storage system. I had gone through this before, but thought is would be fun to double or triple check myself. The company in question makes big, pre-assembled tanks that you lower into a basement or slide into a building with a crane. They also claim they can be buried. Their premise is that this is a seasonal heat storage system. (That is for another day’s discussion.)

So, I ran some numbers.

A 1,000 gallon tank, if built 4’ tall would be 6.4’ square on the base without insulation. If we assume the tank temperature is 140˚F, and the room temperature is 70˚F, the water in the R-32 tank would lose about 1˚F in 24 hours. A R-78 tank water would lose about .37˚F in 24 hours. The numbers go up with hotter tanks and down with lower ones, but in either case, they are not very large.

This is a case of diminishing returns. When considering building a home or other building, there is a point where higher insulation values tend to lose cost benefit. The same is true for tanks.

We will offer higher insulation tanks if someone wants it. It is not hard to do. The cost just goes up. Believe it or not, the cost of insulation is one of the larger costs for any tank.

If you use spray foam to construct a tank, the foam cost doubles over using sheet foam insulation. (We use sheet foam.)

While on the subject of tanks that other companies produce, I am usually answering the question about burying tanks about once a week.

There is a lot of appeal to getting a tank out of the way by sticking it in a hole in the yard. The dilemma for me is that everything eventually requires attention. And polyisocyanurate foam insulation as well as most other building materials can pick up water and lose insulation value when exposed to groundwater. My sense is that if you do not want to lose building real estate to a storage tank, it is better to have a small out building to put it in where it is accessible.

Murphy’s Law rules supreme in the universe, even with tanks.

The Gocze Inverse Theory of the Universe is that if you plan for a problem, it is less likely to happen.

Plastic Heat Exchangers

Many people have asked me about plastic heat exchangers for their (our) tanks.
There has been a ton of research done on this. Many researchers feel that a special injection molded heat exchanger that looks like a car radiator might work well.

We have spent some time on this matter and certainly follow as much research as we can find.
This is a tough design situation.

Just looking at thermal conductivity, plastic is about 1/100 the conductivity of copper.
But, it is relatively thin walled, which helps to overcome some of this issue.

Research indicates that to build a heat exchanger with similar performance to copper, a plastic heat exchanger (I would be considering PEX tubing), would need 4-6 times more surface area.

There is more to it than that, but those are the important numbers.

If you design a heat exchanger to meet this criteria, the cost is about the same as copper, but you will have one heck of a lot of plastic to manage. That is a bit of a hassle.

I am also a little bit nervous about having any PEX connections in the tank over long periods of time and temperature. No one has really done this for very long. There have been incidences of fitting failures (not inside tanks of hot water but at ambient air temps) over the years due to dissimilar materials and crimped connectors.
So far, they seem to be okay, but a couple years does not make a perfect test.

One way around this whole issue is to limit the number of heat exchangers you need.

Heating systems can operate unpressurized. This is being done a lot by outdoor wood boiler manufacturers. It is a little different than a pressure system and works best with buildings that are not real tall.
But it is a simple matter to use a bronze pump to pump tank water out to a heating loop or for that matter to a boiler.
Even though it would be unpressurized and perhaps, somewhat safer, it is important to still include all the normal safety devices.

Another New Tank in the works!

There is always an issue about when to create new products. We either have time or money but usually not both at the same time. When things do line up properly, it is usually fun.

We have been producing some smaller Heat Banks for solar DHW projects. They are competitive with pressure tanks, but I have felt that a small tank could be done better.
We do sell the Softank kit, but it is like a poor cousin when compared to the Heat Bank,
although it has the goods where it counts, in the liner and insulation.

We have been testing a new cylindrical tank that would use our high temp liner and is a lot prettier than the Softank kit. It would be complete with insulation and sets up in about 5 minutes.

And most important, the cost will be lower. I like it when things come together and we can get everything better.

We are currently working on a lower cost heat exchanger for this tank. This is not an easy thing to do given the cost of copper. Copper is still the best deal in terms of affordable heat exchangers for our tanks. And we have refined the design into something that is a lot less expensive than our competitors. That is not a sales hype, it is fact. And the thermal performance is actually better than most other designs.

Depending on how busy Autumn is, we should have this new 120 gallon tank available soon.

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