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Geothermal Buffer Tank Options (8 Posts)
Geothermal Buffer Tank OptionsWhat are the latest thoughts on buffer tank options combined with geothermal water to water when used for radiant heating? We have a large install that requires flow that exceeds the Rheem Marathon 3/4" outlets for radiant supply/return. Has anyone used the storage tanks offered by Bradford White, or similar, for a buffer tank? They appeal as the tapings are very large. The concern is the port location on such a tank, will it affect overall system performance? The price point is very attractive on these tanks. Siggy's geothermal with radiant schematics all show a buffer tank with the ports located 2 on top, 2 on bottom. the Lochinvar buffer tank matches this port layout but the pricing is in the stratosphere.
Buffer TanksI think your other option is the Heat-Flo tanks (which I believe are S/S as well), or a custom made tank.
I worked for a company for 3 1/2 years that used the 120 gallon Rheem Storage tanks that are commonly used for boiler/storage tank systems, as the standard geothermal buffer tank. They'd use the 2 bottom oulets, one on top of each other, one for the return from the distribution, the other for the return back to the heat pump. There was only one 2" top outet of which they'd put a tee on top and pull out to the distribution from one side of the tee, and put back in to the other side of the tee from the heat pump.
There WAS 2 other tappings on the other side of the one 2" top outlet on this Rheem tank - one was a 3/4" tapping, the other was a 1" tapping. The 1" tapping might work if you're worried about having to put a tee in on the outlet of the 2" at the top and having hydronic issues, however they aren't usually issues.
Having said that, the Lochinvar Tanks ARE the go to tank for this application me thinks, along with the Heat Flo versions.
Here is something else to think about - the desuperheater option on most geothermal heat pumps. I personally think it would be better to put a coil (like an indirect coil) on a buffer tank and push your domestic cold through that as a preheat, then to pipe a seperate desuperheater system. The Desuperheater system just adds complication and more potential failure points. If the heat pump only has to worry about the buffer tank, and the domestic can get some preheat through a coil in the buffer tank before going to an indirect, I think that'd be much simpler design wise. You could always use Solar to keep this same buffer tank hot in the Summer when you don't want the heat pump running doing heating to help preheat the domestic water through this coil.Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
QuestionWhat kinds of controls or strategies do you use to prevent the DHW preheat from overcooling the buffer? Or is that realistically not a concern?
Turbomax...They have very healthy tappings (2) and a large coil inside for doing DHW pre-heat, (115 or 120 degrees F) and sizes up to 120 gallons.
pardone' le langweedge...
I have used them numerous times over the years, and have not had any failure issues.
Also, using the two tappings only, I have never had any hydronic issues as it pertain to unwanted flows. You don't want to do a bull headed tee (EVER) unless it is in a prioritized mode. The pressure drop through the tank side of this vessel is so low, that it doesn't matter and doesn't affect secondary flows.
The BEST buffer tank is NO buffer tank at all.. When are the North American GSHP Manufacturers going to get their act together and start providing variable speed compressors based on actual demand instead of utilizing the dinosaur Bang Bang technology? I have actually ceased installing GSHP due to the number of compressor burn outs we experienced in the field.
As for control logics, any outdoor reset logic can be applied to this technology, and it is strongly recommended that you do so in order to obtain the high COP's that are a potential.
PS EDIT, I just noticed that THermomax has also jumped into the buffer tank business. They call it the Reserve
MEIt's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.This post was edited by an admin on January 9, 2011 1:09 PM.
I've done the turbomax preheatbut with the price premium on those tanks, I'd be pretty hard pressed to call it economically viable.
Also, the desuperheater works when you are cooling as well as heating. So a bit depends on whether you are heat only or not. If you are, the buffer tank preheat method makes sense, but a tank cheaper than the turbomax is really desirable in that case.
superstor's "coil booster" tanks appear affordable but still have the tiny taps.NRT.Rob
a few optionsin addition to the ones mentioned. We will have these in 50, 80, and 119 gallon versions. They all have 7- 2" ports around the outside and a few 3/4 on top. also a drain cock. Glass lined steel, 2" insulation, insulated for chilled water also.
I have a small one connected to my wood boiler as a buffer and separator, shown here. We have added an additional 2" port mid tank for more options like gauges or??
buffer/preheatI've done such things a few times: using a purpose built geo buffer tank (mfg by Bock and distributed by NextEnergy in Canada) for the heating and a reverse Viessmann dual coil indirect with the coils piped in series w/domestic going through them. I piped both tanks off the heat pump in parallel with a 3 way valve to switch from one to the other being controlled by a Tekmar staging boiler/DHW controller(can't remember the mod#). This setup works very well, keeps the space heating reset and the DHW tank is always hot. It's preferable to have lower tappings on a buffer tank to promote stratification, keeping the water as cool as possible to the heat pump.
I use these almost exclusivelyWe've been using Boiler Buddy's for two years now. Good tank, easy, and affordable. Like a giant low loss header. No flow restrictions. Good customer service. They are on the other end of the US and I generally get my tank within 3-4 days.