Sidearm Heat Exchanger Not Heating
Hello Everyone! Here's my situation. I've just installed an outdoor wood boiler and it's delivering 175єF water to a stainless steel, double-walled sidearm heat exchanger installed immediately alongside my electric water heater. The bottom of the sidearm is plumbed into the drain outlet of the water heater, while the top end of the sidearm connects to the pressure relief outlet on the side of the water tank. The hookup is just what's needed for proper thermosiphon action, but to boost water circulation through the inner part of the sidearm I have a Grundfos 15-58 circulator on top of the sidearm, drawing water from the bottom of the tank and moving it up to the top connection. A Grundfos 26-99 circulates boiler water through the outer passage of the sidearm. Water flows are opposite to each other – downward flow of the 175єF boiler water, and upward flow of the DHW from the the bottom of the tank to the top. The sidearm gets hot to the touch on the outside, but it doesn't transfer heat to the water flowing through the inner pipe. I know for sure that water is flowing through the inner part of the sidearm (I can hear it flowing if I partially close a shut-off valve at the bottom of the sidearm), but even with the system running all night, and no DHW being used, the tank only gets to about 100єF with the electric elements turned off. I thought at first that the problem might be too much mixing of the DHW in the tank because of the 15-58 circulator, but that's not the case. The tank heats up fine with the circulator running and the electric elements turned on. The more I look at things, the more it seems like that sidearm simply isn't transferring heat. I had originally planned to go with a flat plate heat exchanger in a similar set up to what I have, but opted for a pump-assisted sidearm because of the hard water I've got. The sidearm I've got is double-walled, and perhaps theres a design flaw in this approach. If double-walled means there's some kind of an air space between the inner water passage and the outer one, that sounds like the problem to me. I'm at a loss on proceed. Can anyone offer some insights? I know sidearms work because I've seen them work. Mine is plumbed for thermosiphon action, but it's simply not heating the water flowing through it, even when pump-assisted. Is there anything I can do other than scrap a brand new, $250 sidearm heat exchanger and plumb in a flat plate exchanger? Thanks a million! Steve Steve, I think the problem is that you're pumping the sidearm. The water isn't spending enough time in contact with the hot pipe to transfer any heat... The pump you are using is a BRONZE body one? It should be if it's on the potable water side... but I don't think you want a pump in there anyway. Here's my 2 cents. I have a Central Boiler E Classic 2400 and have the sidearm setup on my hotwater heater along with a 30 plate 4x8 plate exchanger. You may ask, Why both? Well, when I had just the sidearm, we could get 2 showers out of the way and the 3rd person was going to get a cold one. It would then take about 3-4 hours for the sidearm to reheat the 40 gals of water in the HWH back up to about 165-170 degrees. I decided to add the plate exchanger so that as water was running, it goes through the plate exchanger before dumping into the tank. Now, I am dumping warm water into a really hot tank of water. We can now take 4 showers back to back with nobody getting a cold shower. I cannot believe by having a pump on your sidearm that you have cold water! The only thing I might wonder is would the pump serve better at the bottom of the sidearm instead of at the top? From what I recall, a TACO pump cannot suck water. If it was at the bottom of the sidearm, the water would be readily available to the pump and it would simply push it through the sidearm. I don't want to discredit anyone, but I tend to disagree with NJ Trooper only because I also heat my 30' above ground swimming pool and the pump from the filter pushes water through a heat exchanger very similiar to a sidearm at a rediculously high flow rate, I think like 400+ gallons per minute, and the water enters the pool after exiting the HE actually warm. Please let know if you have been able to solve your problem. You're not alone! The only thing I might wonder is would the pump serve better at the bottom of the sidearm instead of at the top? No... wouldn't make any difference. It's basically a closed loop so all you need to do is turn the ferris wheel of water. There's water at both the top and the bottom. Put a pump at the top, bottom or sides of any closed loop system and the performance will be the same. I think like 400+ gallons per minute Good Lawd... how big is that pump, and how big is the pipe? You know that's durn near impossible, right? Highly unlikely. That water would get hot just from the FRICTION of it moving through the pump and pipes! The sidearms for use on water heaters of that type are not intended to be pumped. You can't compare a device intended for heating a swimming pool to one for a water heater. That type of sidearm is intended to be used with thermo-siphon, and that's why it takes a while to work. The water has to remain in contact with the heated pipe long enough to pick up heat from it. Yes, EVENTUALLY the water will get hot. But a sidearm of that type can't be expected to give 140° water when it's flowing past the heated part of the exchanger at several (or MORE) GPM. On second thought though, the actual TIME it might take to heat a tank of water could be about the same, pumped or thermosiphon. I wonder if Steve removed the pump and just let it thermosiphon if he would see the same temp rise in the same amount of time. OR, it might have something to do with the double wall construction as was mentioned? It would be enlightening to know the make and model of that sidearm and look at the manufacturers specs as to it's capacity. It would also be interesting to know the delta T on the boiler side of the sidearm when operating. How hot going in? How much cooler coming out? That would be a measure of how many BTU are being given up to the domestic water side. (same with the domestic side... how cool off the bottom, and how warm off the top? Probably almost the same, my guess... ) It's actually almost the exact same principle we see with fin-tube baseboard... but in the reverse; Let's say you have a heating loop of 65' of fin-tube and pump 4 GPM of 180° water through it. Given the 600 BTU/LF rating of typical baseboard, physics dictates that the water will come back appx 20° cooler. Now, increase the GPM to say 8 GPM. What happens? The water comes back only TEN degrees cooler because there isn't as much 'dwell time' for the water to give up the heat energy. Let's slow the GPM to TWO next. The water will come back 40° cooler because it now has time to give up twice as much heat. OK, I had to go out to the shed to look. Pump for the pool is 70 GPM and exchanger has 2 1/2 inch connections. I have done some research today and opinions swing both ways on the pumps on the sidearm. The ones who have it swear by it, and the ones who don't say don't waste the money. On several HX websites they state you can cut your recovery time of your HWH by 3 to 4 times by adding a pump to your sidearam. I can't weigh in on it because I don't have a pump on mine, but I don't need it. There was something in the instructions while I was setting up my sidearm that it needed to go above the HWH like 3 or 4 inches to make the thermosiphon work correctly. I would like to see some pics of your setup if possible. Have you tried removing your pump. I still find it odd that the outside of your sidearm is hot to the touch but after running all night, your tank does not pick up more temp than 100 degrees. Over time, especially after going all night, it would seem the tank should warm up much hotter than that. Is there any chance there is a obstruction in the sidearm? Maybe the plastic cap they put on the ends got broke and got forced up inside the tube. Steve, here is one of the links I came across which should support your idea of the circulating pump on your sidearm. I still favor either a flaw in the setup or a plugged sidearm. Sidearm Heat Exchangers QUOTE FROM DISTRIBUTOR'S WEBSITE: Applications of the Sidearm Heat Exchanger Due to the compact size and lightweight of the Sidearm heat exchanger these units are ideal for residential heating and plumbing applications. Also called domestic water heat exchangers, they are typically used to heat domestic water using either a conventional boiler, outdoor wood furnace or a solar hot water system. Typically the domestic water is circulated by means of the thermosiphon principle which saves on the cost of a pump and the associated electrical costs. In cases where faster heat recovery is required the domestic hot water should be circulated by means of a pump. Pump circulation will typically provide a heat recovery 3 to 4 times greater than thermosiphoning. I did a little reading the past couple days on these things... Have seen widely varying BTU output numbers for essentially the same size unit, from 8000 BTUH to 22500 BTUH. One manufacturer says that their 8K unit will output 12K if pumped... at TWO GPM. I am absolutely certain that even on LOW speed, the15-58 G'fos pump is at the very least pumping at 6 GPM, and I think that's a conservative estimate. MORE flow does not necessarily equate to more BTU, even IF pumping a domestic sidearm will increase it's capacity, (it IS after all, a function of SURFACE AREA , thermal conductivity , and DELTA T that determines the transfer. If the pump improves this, it is probably because it adds TURBULENCE to the flow, thus increasing the transfer rate) and there MUST be a point of diminishing returns. I believe a domestic hot water recirc pump would be MORE than large enough to flow 2 GPM through the sidearm. AND it will be BRONZE, which I don't think Steve's 15-58 is... but he's not been back to answer that question. Hit and run... I SERIOUSLY doubt the claims of the manufacturer that says pumping will provide 3 to 4 times faster recovery. It may even be the same manf that says pumped is 12 K ... only one and a half times more BTU output... how can that possibly equate to 3 to 4 times faster recovery? Let's look at a 40 gallon WH. There's 320 pounds of water in there. Let's say the incoming water is 60°F and our target is 120. That's a 60° rise. It takes one BTU to raise one pound of water one degree. Therefore, to raise 320 pounds 60 degrees you would need to input appx 20K BTU into the water (assuming no new water added, no use, say overnight) So, with an example HX of 8K BTUH in thermosiphon mode, you would be looking at a little over 2 hours to heat the tank. If the 12K figure is to be believed, you would be looking at a little under 2 hours. In either case, recovery time is going to severly suck. Two quick showers back to back and yer gonna have to wait another two hours for a third. Sidearms have their place, but don't disconnect the electric elements! Yer gonna need them! Even so... with that thing running all night, and 175° boiler water flowing the whole time, I would expect the temp to be higher than 100. It probably should have easily been at 120, and I would expect even higher. Don't forget too that as the water in the domestic tank approaches the temp of the boiler water, the heat transfer is gonna slow WAY down... that's the DELTA T part of the equation. I just had another thought... in a typical water heater, you really don't have 40 gallons of water heated to SETPOINT. With a thermostat near the center of the tank, your AVERAGE temp in the tank would be at the setpoint. Hotter on top, cooler on bottom. Pumping the sidearm might have the advantage of providing MORE water at setpoint because of the 'mixing' that goes on. I would think that pretty much the entire tank will be at the same temperature. There's a downside to this though... if the pump happens to be running while the hot water is being drawn, the entire tank will also cool down at the same time because of the same mixing... cold water entering the tank gets pumped and mixed to the top of the tank. This doesn't happen without a pumped sidearm... the hot water is drawn from the top while the bottom is filled with cold. There's little mixing of the incoming water occurring. Let's see if Steve comes back and tells us that the single wall model the manufacturer agreed to send him works any better. By the way Wayno, no problem disagreeing... it causes me to think and substantiate my statements... I like an intelligent discussion! There was something in the instructions while I was setting up my sidearm that it needed to go above the HWH like 3 or 4 inches to make the thermosiphon work correctly. Check those instructions again... if there's a loop coming up off the sidearm, over and down into the tank on top, you are creating what is essentially a 'heat trap'. The taller the up and over loop becomes, the LESS the thermosiphon action. The heated water will rise to the top of the loop, but not flow back down. The IDEAL connection points for this type of sidearm would both be on the side of the tank, high and low, not on top. You want to MINIMIZE the height of the pipe on top of the tank as much as possible for maximum thermosiphon action. NJ, I just had those instructions out last night. I wish I had taken a snapshot to post. I have a couple pics of my system. My system works flawlessly. You will notice my temp gauge is showing around 170 when pic was taken. Usually fluctuates between 170 and 179 depending on use at the time viewing it. Also, it is a clip on thermostat so temp is likely seveal degrees warmer than stat shows. I'll dig those instructions out tonight and see what they say. I wonder if it said within 3 of top? I'll let you know. Below are links to my pics Pic 1: http://websites.networksolutions.com...=1334846254634 Pic 2: http://websites.networksolutions.com...=1334846383788 Pic 3: http://websites.networksolutions.com...=1334846344914 I looked at the sidearm installation instructions last night and it says to extend no more than 3 to 4 inches above the DHW heater. So NJ, you are correct in saying you should stay close to the top of the tank.
Related Posts:
Sizing a flat plate heat exchanger
Sizing a Flat Plate Heat ExchangerHello Everyone! I need to know if there's anything beyond the obvious when it comes to choosing a flat plate heat exchanger for a hydronic heating installation th...
Trane xv90 furnace heat exchanger
Trane xv90 furnace heat exchangerThere are other dealers out there that would probably honor the 10 year parts warranty, do you have the labor warranty too? Hi I've posted here before just in anot...
Tankless bosch aquastar 125b ng water doesnt heat past lukewarm
Tankless Bosch AquaStar 125b ng- water doesn't heat past lukewarmMy tankless water heater started acting up a couple of months ago and sometimes would not heat the water to warm. But in the last 2...
York diamond 80 furnace doesnt shutoff and doesnt heat
York Diamond 80 furnace doesn't shutoff and doesn't heatI have had this problem intermittently for 2 or 3 years. My furnace quits blowing heat, when set to heat and setting is higher than room tem...
Well drilling cost for geothermal heat pump
Well drilling cost for geothermal heat pump1. Anyone know a ballpark figure for getting wells drilled to setup a geothermal heat pump? 2. I've heard good things about geothermal heat; however, my...
