I still have a few questions about how best to heat DHW. Superstor probably the best option but in my case I would still like the electric to take over in the summer months or in cases where I let the storage cool too much. Even one cold shower and I would probably never hear the end of it. Superstors are expensive (>$1000) and not something you buy when you already have a new electric tank type. Many are using the flat plates now with a flow switch to make an on demand heater kind of like the new gas fired tankless ones that have recently became popular. While I see this working fine for the most part, I still see a few times on a gasser/storage setup where the storage gets too cold due to a missed firing or a larger than expected demand (ie. dishwasher, extra laundry, jacuzzi bathtub). I saw this Ebay Sidearm that looked interesting. It has 7 small tubes with an 1 1/2" outer tube that is only 13" long compared to typically 48". The claim is that the extra tubes gives the extra heat transfer making the long tube unnecessary. Also they claim that the short HX allows for better thermosiphon action compared to a full length sidearm. I'm assuming they mean you can mount it closer to the bottom of the tank which should improve the flow. One thing that concerns me is the possibility of a leak which would be disastrous. I would think even the plate HXs have to potential of this happening. I'm guessing on a Superstor the piping is continuous without any joints touching the DHW making it very safe. On an old style sidearm the only danger of a leak would mean a mess on the floor not contamination of drinking water. Unfortunately the way they made this one it looks like a failure on the solder could be disaster. If the properties of their design really does improve heat transfer and thermosiphoning, I wonder how an improved version of theirs would work moving the connection of the 7 smaller tubes into one DHW fitting outside the 1 1/2" pipe holding the boiler water. Bottom line the 7 small tubes would be completely continuous where they touched boiler water. Worse case of a solder failure would be boiler water leaking on the floor, not contamination of the drinking water. Maybe I'm too cautious but I don't like taking chances when I don't have to. I would rather stick with electric DHW than have a 0.1% chance of failure. Any thoughts?
Different type of sidearm?
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That is an interesting sidearm, I would have the same concerns as you mentioned about leaks.
I have the "typical" sidearm installed, it works okay but in hindsight I think putting a plate heat exchanger on my cold water inlet on the dhw tank would have been a better option for me, simply because I would not need to worry about boiler water temps. I could make some fires in the summer without being concerned about keeping it up to 140 deg. It wouldnt need to heat my hw to 140, simply preheat the cold water coming into the tank and let the electric bump it up to temp. I may still add this exchanger someday if I feel the urge to do more piping (gonna be a while, i have had my fill)
I have the "typical" sidearm installed, it works okay but in hindsight I think putting a plate heat exchanger on my cold water inlet on the dhw tank would have been a better option for me, simply because I would not need to worry about boiler water temps. I could make some fires in the summer without being concerned about keeping it up to 140 deg. It wouldnt need to heat my hw to 140, simply preheat the cold water coming into the tank and let the electric bump it up to temp. I may still add this exchanger someday if I feel the urge to do more piping (gonna be a while, i have had my fill)
Any plumbing fixture/connection has the potential of leaking whether it is pressurized or not. (Ask the seller if the "new concept" sidearm has been pressure checked and to what pressure and how long.. Perhaps that will alleviate the leaking concern) The concept of the "linked" sidearm is ideally correct in the amount of surface area they get. If the diameter of the large pipe is sufficient to deliver the needed flow with that much displaced area then it should be a good unit if it is installed low like you say. The only reason other sidearms are 48" or so is to transfer heat. Large diameter interior pipes are not going to transfer heat as well as the linked unit because they have less surface area involved and surface area is needed to transfer the heat. Smaller tube will cause a better mix inside of the tube and so will heat the water more quickly. Though it may not be necessary mu gut instinct is to have a longer sidearm than the stated 14". Another concept for heating the DHW is to use a plate heat exchanger going directly in to the hot water tank (in place of the cold fill water) instead of bypassing it. That way any time hot water is taken out of the DHW tank it is immediately replaced with pre heated water. Since the fill tubes of a DHW tank deliver water to the lowest part of the tank the electric will not come on until the boiler side of the plate exchanger gets too cool to heat the incoming cold water and the fill water gets below below the DHW tank setting.
infinitymike
Minister of Fire
does anyone have any pictures of a sidearm setup on the unit?
I don't understand how it works or how its piped.
I don't understand how it works or how its piped.
No picks imike but basically a pipe T's out from the water heater drain plumbing and T's into the water heater over heat/pressure line. That pipe is enclosed by a larger pipe that boiler hot water is pumped through. A water pipe inside of a water pipe. The two waters never meet and the boiler water heats the DHW through convection. Looking at the link supplied by huskers who started this thread the pipes going out from the ends is for the water heater and the ones going out of the side are for plumbing in the boiler. As stated above most sidearms are around 4 feet long and the one in the link is shorter but offers more area for heating the water but with a multiple element in a shorter version of sidearm heat exchanger.
infinitymike said:
No pics, but I might be able to help with the rest.
Essentially, you pipe this thing into the side of an existing domestic hot water heater. You would connect a pipe from the port on the top where the pressure relief is, and put that into one port of the sidearm. Another pipe goes from the bottom of the sidearm to the drain valve on the hot water tank. (You relocate the pressure relief and the drain valve when you do this). Now what you have done is made a loop that goes from the top of the tank to the bottom of the tank.
Then what you do is connect water from your boiler to the other big ports on this sidearm. When you need domestic hot water, you pump through this thing, and it circulates water through it. Since its a tube within a tube, the boiler water flows around the outside of the pipe carrying domestic water, which is the smaller one (or in the case of the eBay link, its the 7 smaller ones). This causes the water to get hot, and rises to the top of the tank. Since this rises, its replaced by cold water, and that then gets heated until all of the water in the tank is happy and you stop pumping boiler water through it.
The house I rented had an OWB and they just pumped through a sidearm before it ever got to the zones. That way there was always plenty of hot water no matter what.
A couple more things to mention. Although not everyone does it, it is highly recommendend to put a mixing valve (like this one) on the output of the water heater toward the home distribution because the water can become as hot as your boiler gets, especially if you circulate using a loop to other loads like some have mentioned. the mixing valve takes the hot output of the tank, a tap off the cold line and mixes down to a safe temp like 125 to prevent scalding. Imagine what would happen if your kids took a shower with 170 degree tap water. My setup would have its own circ off my house loop (closely spaced tees) to and probably a aquastat to prevent it from heating the top of the hot water tank above about 160. Since I use storage I also don't want it to run when the temp at the house loop is less than the DHW tank itself, so that requires a differential controller possibly like one of these that are pretty reasonable. I think I will sketch all this out including an "improved version" of that sidearm on the first post. My version would have the 7 small tubes exit a capped 1 1/2" outer tube (containing the boiler water) a few inches on both ends before expanding back into a single 3/4" (code I believe) water line on both ends. This way it would be like a Superstor or old style sidearm were the boiler water only touches virgin copper tubing and doesn't rely on the integrity of a joint to separate drinking water from nasty water. Maybe overboard to some but probably a reason why Superstors are built this way.
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