Keeping your buffer tank tempetature down

A.J.

I have to install a geothermal piece of equipment for some radiant heat (low temp.). I'm resetting the buffer tank and using a boiler for some aux. heat but for the life of me I can't figure out a good way to pipe the return to keep the buffer tank temperature down below 120 deg. I would like to keep the geo. going even when the boiler is on to increase efficiency but how do I keep the buffer tank temperature from creeping up when the boiler is running thus possibly locking out the geo. equipment .
Thanks

Henry_6

Buffer Tank Reset

The best method to set a buffer tank is by outdoor reset. You can operate the geo system strictly on outdoor reset based upon demand curve of 3/4 degree rise for each one degree drop. I would never exceed 120f to the floor unless you have carpet acting as an insulator. To prevent the system from cycling off due to high temp, have an adjustable high limit(such as Johnson p20 series control designed to cycle off the compressor (only) when the forward line temp is > than 125f. Set the adjustable differential to 10f and you will always have perfect heat. This works in cold climates and is very reliable. If you are using the system for chilled water in the summer, and why wouldn't you, set the high limit to operate for heating signals only. Where are you located?

Mark Eatherton

You can't...

Even if the buffer is parallel to the load, if the auxillary unit is on line generating water temperatures greater than 120 degrees, the HP is going to shut down, which at that point you want it to do unless you are also doing DHW preheat, in which case the DHW preheat should be piped as a separate vessel.

I have done many "hybrid" systems, which is what you are describing, and if they are both going to be on line, at some point, only one of them is going to run. Done properly, the system SHOULD have been designed around the maximum temperature available from the GSHP system. If you need temperature higher than the GSHP is capable of delivering, at design conditions, then only one unit can be on, because if your supply is running out at say 140, the return is coming back at 120, it will shut your HP down.

On a recent 25K sq. ft. hybrid we did, I convinced the HO not to place his massive, thick throw rugs on his hard tiled floor so he could operate on the HP more than the boiler, and he made it through the winter, comfortably, on his HP only. The boilers are doing DHW top off only.

You can have a simple outdoor reset controller for the GSHP, and then "nest" the control logic of a modcon boiler into the scenario, and if the GSHP is capable, it will generate water temps high enough to keep the boiler off line.

I'm betting that you are like 90% of the contractors out here who are conservative, and the system is actually capable of doing a lot more with low water temps than you give it credit for...

K.I.S.S.

Best of luck.

ME

scott markle_2

25k sq.ft K.I.S.S is a punch in the face.

Mark,

Nothing personal but, 25k btu would be a nice design load.... 25k sq.ft should be illegal. No level of Hybrid mechanical efficiency can justify this.

Some of us are wondering how things have gotten so bad so quick, has our collective security has been stolen and squandered. Do these kind of homes represent the spoils of a corrupt financial system. Are "we" now paying the price for these false fortunes?

We can't liquidate mansions to run schools and feed people, what happens when the "natural" capitol runs out in 30 years or so. Will the Chinese keep buying our treasury bonds when the petrol fueled economy finally hits it's ecological road blocks. Imagine the indignation our children will feel looking back at the decisions we made.

Mark Eatherton

Sorry Scott...

I don't design them. I just keep the people inside comfortable.

This guy is one of the largest off shore oil well drillers in the world.

Need I say any more? He was whining BIG time when the oil prices started dropping. Did I feel guilty enough to want to give him some of his money back? Shirley, you jest....:-)

At present, he does not have a drill bit turning in the Earth. I don't feel the least bit sorry for him. I do feel sorry for all of the employees he has that aren't doing squat.

About the time we start telling people what they can or can't build, we might as well call our selves the United States of Russia...

Free market enterprise at its best, and trust me, this guy gives millions back to the community in the form of contributions in kind. He sleeps well (and comfortably) at night.

ME

A.J.

Low buffer tank temperature

I'm around the Altoona Johnstown area of Western Pa.
The supply water should only have to go no higher than 102 deg. if I remember the report right,but I am still need about 15K aux. at design. I was planning on running reset buffer tank water through a G115BE and letting the Logomatic monitor the temperature along a reset curve to decide when to fire the burner. Looks like I need to rethink that. GSHP seems like shuts a good fit for low temp. radiant.
Since this is my first water to water GSHP I'm getting a little nervous.
Thanks Guys !

Mark Custis

AJ folks,

just do not like water to water. Then add heat pumps they panic.

Call me if needed what you are doing will work well.

Now if I can work the lotto this will post.

Craig R Bergman

Scott

What that man chooses to do with HIS money is none of our business!! Do I agree we these monsters? No! I think they are foolish and wasteful. As long as we live in a representive republic and not a Marxist state he is FREE to do as he wishes. Just as you are!

Bergy

Craig R Bergman

Scott

What that man chooses to do with HIS money is none of our business!! Do I agree we these monsters? No! I think they are foolish and wasteful. However, as long as we live in a Representative Republic and not a Marxist State he is FREE to do as he wishes, Just as you are!

Once we do live in a Marxist State, only those in power will be FREE to do as they wish! So, be careful what you wish for...you just might get it!!!

Bergy

[Deleted User]

Parallel curves

If you set both curves up identical to each other, if the GSHP is capable of carrying the load, the aux boiler will not come one. If the system gets slammed by a cold slab load and is uncapable of maintaining required temperature, boiler will blend in and help push the load over the hill. However, I would recommend that you consider using a modulating/condensing boiler, otherwise you will significantly overshoot your target and cause the heat pump to stay off line longer than it should. Plus, it allows the modcon to do only what is necessary in a proportional mode, not a BANG BANG mode.

Instead of running two separate ODR's, just run one 2 stage ODR and lock the aux boiler in as the second load. THe only disadvantage to this is that it will have the chance to "mask" a problem with the GSHP, and the problem will not manifest itself until it gets REAL cold outside, and the only thing running is the aux. boiler, but I guess that could happen with the parallel curve idea as well.

Your required operating temperatures at design condition are well within the capabilities of the GSHP (max 115 recommended). Don't be afraid. Jump in with both feet. If you start getting in over your head, we're here to throw you a life line. Just make darned sure that whatever goes into the Earth has adequate capacity. That is the one thing that CAN'T be easily fixed...

ME

J_13

Boiler Connection to GSHP

Connect the boiler with closly spaced tees on the supply piping from the buffer tank. Utilize the boiler as a fixed last stage. Outdoor reset on the tank & boler. I have done this on several projects & it works well. I have also used variable speed injection on a couple for very accurate temperature control.

A.J.

Thanks again

We are finishing up with the plumbing rough this week so I expect to start working on the heat again in about two to three weeks, so I just wanted to be sure of the last lose ends. I have even been hanging around waiting for the mailman to deliver the mail not for the checks but for part three on ME alternative energy interfaces (that a great resource ),thanks Mark. There have been some bad installs in our area in the past from guys trying to get started in GSHP market. I just want to make sure that I am not one of them. The best time to trouble shot is while everything is sill on paper.