Radiant Geothermal Control

Unknown

the pump would run on any heat demand. just that the geo compressor doesn't run until we actually need it to.

I just hacked together this drawing, but technically we are "pumping away"; positive pressure goes through the load, and pressure drop from the expansion tank to the suction side of the pump is practically zero. not exactly zero, but it would be pretty hard to induce air to come out of solution in that return header. this sort of placement would be done only if site conditions warranted it.

and I was at REX, sorry I missed you rich! I missed a lot of people I wanted to see.. just not enough time in a day, and not enough days. I did miss a couple of group gatherings too that might have made a difference.

Nick S

I have a job coming up that will use a water to water geothermal heat pump with radiant floors for heat, and a chilled water fan coil for cooling. I am familiar with radiant design, mod/con boilers, outdoor reset, etc, but I am having a hard time with this project. I am looking for some way to control this unit with 3 or 4 radiant zones with outdoor reset, and 1 zone for air conditioning. Does anyone make a control like a Tekmar for these things? Also, can you guys point me to a buffer tank manufacturer. Thanks for your help.

Unknown

www.heat-flo.com

for the tank...

I think all the various tube mfgs have ways of zoning at their manifolds. I'm sure they'd help you get going in the right direction. Given your already low operating temps outdoor reset might be overkill.

Unknown

I don't think reset is ever overkill for geo. every ten degrees you can drop counts for big, big gains in geo.

If you have a pump separate from the geo unit, and a buffer tank on the geo supply line, I'm thinking primary/secondary and treat it just like a boiler with the supply sensor after the tank is the way to go. With a good buffer a mixing device shouldn't even be necessary for a one temp system.

van_8

geo control

B & D Mfg. makes a non-pressurized stainless steel buffer tank that will do what you are looking for it comes prewired for heating and cooling very nice product.
www.bdmfginc.com

Nick S

Why non pressurized?

Unknown

it's cheaper. except for the pumps, of course. and the replacement pumps later. but the tank is cheaper, at least. I think

I don't see a reset control built into them either.

Nick S

This is what I was thinking as far as piping it. But, because this is a heat pump with more terminals than "R" and "W", and I need to control the unit for cooling, I am not sure what to use for the "Temperature control". Maybe the B&D unit is the way to go, but I'm not sure I am sold on the non pressurized thing. Courtesy of Siggy, http://www.radiantandhydronics.com/RH/Home/Images/1007-portal-GF-Fix-lg.jpg

van_8

There are many benifits to non- pressurized hss tanks less install time wiring all done wire t stat to control fewer call backs due to lost pressure in the system can be piped with pvc,if header is inside no need for purge cart just to name a few.

Unknown

heat/cool thermostats, for one, though if you are doing chilled water, minimize the piping it will run through.

we're using 420's or basic boiler reset controls with buffer tanks around here. pressurized and closed, of course.

Jeff Hammond

Geothermal/Radiant controls

I work for a geothermal heat pump manufacturer, and I get this question at least once a week. Radiant floor with geo is fairly straightforward, as long as you have a buffer tank. When chilled water cooling gets added in, it becomes much more complicated. I agree that outdoor reset can provide significant savings, especially when you consider the COP at 90F water vs. 110F or 120F. I suggest that you handle the cooling separately. The reason is that there's always the switchover issue. For example, if your buffer tank is hot and your radiant floor is warm at night, there's always the possibility that in the Spring or Fall, you may need cooling during the day. In large, expensive homes, those type of customers want heating and cooling when they want it. It's like a two pipe system in a commercial building. You either get heating OR cooling, and you have to decide when to switch over. One of the ways to get around this is to use a combination unit (i.e. a water-to-water and water-to-air in the same box). This allows you to use the water-to-water portion for radiant floor heating, and the DX cooling side for air conditioning. Even better, you could use forced air heating in the Spring and Fall to avoid having to keep a warm floor and buffer tank. When you separate the heating and cooling systems, the controls become much simpler. The radiant floor controls turn on/off pumps and zone valves, pulling hot water from the buffer tank. The outdoor reset control determines the buffer tank temp. The heat pump (water-to-water portion) only "cares" about keeping the tank at temperature. Then, in cooling, a standard cooling thermostat controls the heat pump's DX cooling side. We've used Bock and B & D buffer tanks with a lot of success.

klaus

Controls

I used a control manufactured by Geo-Tech Corp. out of Dubuque, IA on my home. It's a packaged controller that has three sensors, Geo discharge temp, used in cooling mode to a fan coil, tank temp, used for heating, and an outdoor temp sensor, used to control heat to the fan coil for shoulder seasons when you want to avoid the flywheel effect of the floor mass. I've also added outdoor reset (not shown in the picture) to it to improve efficiences and floor comfort. After adding this I wouldn't be without it.

The guy who came up with this controller was a local Geo-contractor who couldn't find a control to do the things he wanted so he designed his own. It interfaces with a regular thermostat and has seperate connections for t'stat, geo unit, and fan coil unit. I like it for the most part but had to have a few conversations with the designer to get everything setup originally.

If I were doing it all over again I would probably use one of the all in one units mentioned above to provide hot water for floors and forced air for cooling. I think it would be a much simpler and quicker install.

Good luck, Rich L

[Deleted User]

Questions for Jeff Hammonnd...

Why is it that a buffer tank is required for W-W heating system, but not required for W-A cooling system?

I just commissioned a system with W-W heating and cooling capabilities in a 25,000 square foot home here in Denver. We used a Thermomax reverse indirect tank for space heating/DHW preheat, and a seperate tank for chilled water application. We used 2 heat pumps at 5 tonnes each, and a tekmar 2 stage control for both heating and cooling, and prioritized the cooling calls over the heating calls unless heating is already engaged.

When are you guys going to embrace the direct digital control age and start doing variable speed compressor motors using the ECM technology that the rest of the industry has been using since, forever?

I HATE short cycling compressors...

It's OK to tell us what manufacturer you work for as well... Just be prepared to take some heat if your company has "issues" out in the field.

But where better can you learn about solutions than the Wall?

Welcome to The Wall.

ME

Unknown

I would vastly prefer not to maintain the buffer tank temperature. If you do, it's not a buffer tank, it's a storage tank. There is no reason to maintain a tank temperature if you don't have a heat demand, is there?

Unknown

heating Only setup

Is there any downside at all in the sample I have attached?

It seems to me to do everything you need (maximize buffer, reset control draws down the tank before firing the geo, minimize return temps as long as possible) and no real downsides, unless your geo system has a built in pump you have to "hack" to run independantly....

With the teknet 4 control you really get to minimize those operating temperatures too...

BC_5

Rob

Would the geo pump run continuously? There are 2 potential problems with this. Some w-w heat pumps (mine included) have what I consider an undersized heat exchanger on the hydronic side with a high pressure drop. As a result to get the required flow I need over 350W of pumping power (and this is with very efficient Armstrong pumps). That's a big load to run all the time. The other potential consideration is that heat pumps may not like having water circulated through them when they're not running as it can cause refrigerant migration. I beleive it's mostly a problem with running cold water through the hydronic side, so it may not be an issue for a heating only setup.

What's the advantage for this setup compared to simply pulling radiant supply from the top of the tank and returning it to the bottom independent of the heat pump loop?

Tom Romberg

Jeff Hammond

Hey old friend. Looking for your new contact information. My daughter found this site. Please contact me! Thanks,
Tom Romberg

Unknown

Hey BC,

I must have missed your response, sorry.

we would only run the geo pump on a heat demand, and fire the geo when heat were actually needed, using indoor/outdoor feedback to determine that temperature.

so we could circulate when the system was not firing, but only during heating periods (for now, at least) and only when it is heated to some degree at least.

the goal here is twofold:

1. maximize buffer capacity by not maintaining storage temperature

2. Maximize geo efficiency by turning it off before making it work too hard with elevated water temperatures we don't need

3. Minimize return water temperature to the geo for as long as possible.

we have used buffer tanks as hydraulic separators in other systems, but I don't like that for a couple of reasons. One, some mixing occurs in the tank, so return water is not necessarily as low as it could be. and, the flip side of that coin is that if you are NOT mixing, you are not really utilizing the full capacity of the buffer tank to buffer.

and i HATE maintaining tank temperatures because it again reduces buffer effectiveness during low load scenarios and also, without reset it should be way less efficient most of the time, and with reset I still don't see the benefit compared to a "fire when needed" only system.

but, I am not a geothermal expert either! What do you think?

klaus

W-W GEO

Hi Rob, Were you at Rex? I met a few Wallies there, would have enjoyed meeting you if you were there too! I really enjoyed the presentations.


I like to set-up my w-w geo systems with a warm buffer tank any time the heat is on by the t'stat, regardless of the call. I also prefer to use a simple outdoor reset control in the system for heating. By doing this I greatly reduce the lag time waiting for hot water from the buffer. By using the ODR as well I'm keeping the tank as cool as outdoor temps will allow to maximize efficiency. I'm sacrificing some efficiency to minimize reaction time.

For cooling I pull right off the discharge of the GSHP and send it to the coil in the air handler. I only bring on the GSHP on a cooling call. By doing this don't need to keep a cold tank all the time.

klaus

One more point

on your schematic Rob. If your geo pump only runs when your sensor calls for heat, how are you going to get that warm tank water to your secondary curcuit? Isn't your secondary going to just make the short trip around itself? What's going to move the heat out of the tank without the geo pump? On a side note, is that where you'd place your exp tank, air seperator and fill? Why wouldn't you want them immediately before the circ pump (ala "pumping away")?

Unknown

I would recommend...

I pipe heating only geo systems like thus with great success. The piping works much like an oversized low-loss header, offering not only short cycle protection for the heat pump but complete hydraulic separation between the heat pump and your system as well. Make sure you have your reset control's supply sensor well imersed in the tank, I usually remove the anode and insert at least an 8" well in its place.

Unknown

why the concern for reaction time? couldn't you just use a smaller buffer?

Randy Calvi

geo reset controls

I had a similar problem with a combo high mass radiant floor and fancoil cooling setup. The Tekamr controls for boiler reset are fine for heat only systems, but get kind of clunky when you start adding cooling functions. I found a geo control that gave me what I needed for this specific project and maybe it will help you. The company that makes it is HBX Controls (google it and you'll get their website) and the unit is an ECO-1000. It is an either/or geo/solar controller and includes three sensors. It's a little spendy, but gives you reset, staging and rotation, auto changeover and several other functions all in one unit. It's also expandable for up to 14 stages (I think). I'm still in the final stages of the project, so I don't have all the final programming finished yet, but so far works great. I also have three Tekamr tN4 thermostats and a user switch so the customer doesn't have to know how to do anything except push the "Occupied" button to change schedules and functions. AND they were willing to pay extra for it! How often does THAT happen. Anyway, maybe that'll be a helpful resource for you. Email if you have any questions.

Sincerely,

RC

Unknown

my theoretical objection to this is that you are not utilizing your full buffer capacity unless you cross pipe the buffer tank. If you did utilize the full buffer capacity, then mixing in the buffer should raise water temps to the geo faster. do you agree, or am I crazy? not that the two are mutually exclusive!

klaus

Smaller buffer-

Nope. You're limited by the size of your GSHP. Standard rule of thumb for the buffer is 10 gal/ton of HP minimum. 2-1/2 ton heat pump - 25 gallon buffer tank, 5 tons - 50 gallons, etc. This helps keep the compressor from short cycling.

[Deleted User]

Yeah but...

Rich, you said you were running the chilled water direct from the chiller to the fan coil, no bufferin...

Why is it OK to short cycle on cooling but not heating? In my experience, the cooling loads are typically a LOT less than the heating loads, hence more potential for short cycling on cooling. If anything, in my estimation, a chilled water buffer tank would be 2 times as big as a heating buffer...

No??

ME

Did I misread something here?

Unknown

rich, did I see the words "rule of thumb" cross your keyboard?

you can do better than that

edit: if you are concerned with reaction time, that would mean your buffer is oversized for your geo system/operating delta T. If it is not oversized, reaction time shouldn't be a very big problem. I think!

klaus

Misread

But then again, maybe I wasn't too clear!

"For cooling I pull right off the discharge of the GSHP and send it to the coil in the air handler."

I pull off the discharge, not send the discharge fully into the coil.

To clarify Mark, I put a Tee on the discharge line of my GSHP's between the unit and the buffer. I use a Taco EBV valve and a pump on this line direct to the fan coil. I pull as much water off as I need to get proper Delta T at the coil (3 speed pump) in cooling mode. (Went back to the coil mfgr to get that #, thanks ME!) My cooling sensor goes down stream on the discharge line just before the tank. This way I'm not trying to maintain a cold tank and get the coldest water to my AHU coil. If I'm not using all the chilled water supply, and I'm not for the reasons you stated above, my tank eventually catches up and cycles the unit. Now I'm still pulling low off the tank, getting the cooler water and giving the HP a longer off cycle. My return from the coil ties into my return from the radiant floor loops and goes straight to the tank. In effect, for cooling I'm increasing the size of my buffer by not directing the full stream of conditioned water to the buffer. Make sense?

BTW I saw you at your booth at REX and stopped to introduce myself. You were explaining your window to several others and I figured I'd just stop back, I wanted to hear the full story myself! Anyway I didn't make it back, had to drive back to Iowa early for an unplanned family matter. Hopefully next time!

klaus

Caught me!

I thought I might get called on that statement Rob! Imagine you being the "caller"!

That said, that's a widely accepted "sizing guide". Better wording?

I don't think you can oversize a buffer tank, IMHO, within reason. The larger the tank, the longer the cycle times, the happier the compressor.

I think if you could accomplish those goals Rob, which I believe is what you're trying to accomplish, without running the GSHP circ pump, your temp controls would be a great idea, for all the reasons you mentioned above. Just my 2 cents.

Thanks for keeping me on my toes!

Unknown

why avoid the running the GSHP pump, electrical usage or this refrigerant migration issue someone mentioned?

Jason Jimenez

Storage tank vs. Buffer tank

I have a similar scenario as you stated on this post, and the main question i have for now is how do i know if the propper installation should be to install a buffer tank instead of a storage tank?

klaus

Electrical

usage AND lack of hydraulic seperation. Stated above, generally takes a good sized pump to give proper circulation through the GSHP. Why run two pumps if you don't need to? Is hydraulic seperation absolutly necessary, no, but you've got the perfect seperater right there, why not use it?

Refrigerant migration will be a non-issue in heating mode. Condenser (in heating mode) won't attract refrigerant.

I don't understand how you'll draw the tank temp down further with your piping arrangement. Looks to me like either way your circulating through your buffer. Won't you pull the same amount of heat out of there to meet load requirements either way? What am I missing Rob?

Unknown

the theory is:

I am not "polluting" my geo return water with geo supply water; it gets only coldest possible tank water, mixed with radiant return water, to send back to the geo. In a true "buffer hydraulic separator" situation, the geo supply water can mix back in with the geo return water, raising its temp. OR, if radiant flow rates are higher than geo flow rates, you lose a lot of buffer capacity because you're not heating the whole tank before you trip out your water temperature to the radiant.

I'm not drawing the tank temp down further, necessarily, it's simply a question of how fast the return to the geo heats up and how hot it gets, and how much buffer capacity i'm using. but you might be right, it might not make a huge difference... still noodling.

Jeff Hammond

Reply to Mark Eatherton

Mark,
I was just re-reading the responses on the geothermal radiant topic, and I have to apologize. I completely missed your posting that said "Questions for Jeff Hammond." It looks like a lot of people have responded since. If you would still like my response, let me know. I think I have hang of this bulletin board now. Sorry for the confusion.

Regards,
Jeff Hammond
jhammond@enertechmfg.com

Ted_5

HBX ECO-1000

That is the cat's meow for controling ODR on heating and setpoint cooling with auto change over. We have found it is not that expensive compared to other panels made to do the same functions. try it you'll like it!

Ted

Paul Rohrs_4

Ditto

A rep in my area just picked up the line and I pencilled the ECO-1000 control in on my next job. I called to chat with Tech support and was TOTALLY impressed. They also have Visio stencils for drawing out systems.

Regards,

PR