I have a two year old climatemaster geo system that consists of three units for a three floor structure (2 ton, 3 ton, 2 ton). Here are my desuperheater questions: 1. My desuperheaters are currently plumbed in series. I've read on a different thread that they should be plumbed in parallel. Why? 2. Why is PEX not recommended for desuperheater plumbing? Thanks. Dan

Parallel so that all desupers access the coldest available water.

A desuper pump failure or other circumstance could cause desuper plumbing to experience temperatures that exceed the upper temperature rating of Pex

Posted By engineer on 01 Feb 2014 12:46 AM
Parallel so that all desupers access the coldest available water.

A desuper pump failure or other circumstance could cause desuper plumbing to experience temperatures that exceed the upper temperature rating of Pex

Agreed

Here's what you're looking for...

I have this picture taped to the front of the larger of my two WaterFurance Envision units.  Someday I'll connect both of my Envision unit DSHs together, per this diagram.

This is another 'Bergy' diagram that's been posted a lot, and would have my vote to include in a GBT 'Hall of Fame' postings.

Thanks Bergy!

Best regards,

Bill

Bill et al. I am really confused by the continual honouring of this layout. It is only the geo industry that uses this. The solar and radiant industries go to great length to make sure a buffer tank stratifies yet the experts on this forum all seem to agree with this method.

If you go to Skyheating's wel server, you will see that his set up only raises the temp around 5 degrees. This is not even worth install the dsh let alone the buffer tank. If you spend a little time on the wel site reviewing some of the setups you will see that any tank set up this way produces very little energy. The one set up to take cold water from the bottom and sent the hot from the dsh to the top of the buffer produce lots.

Careful review of Skyheating's site will show that some of the hot water introduced at the bottom of the tank is sucked right back up the dip tube to re-feed the dsh. Any heat that escapes the dip tube suction works its way through the tank agitating all the water so that basically the whole tank is the same temperature.

The standard in the radiant and solar industries when using an electric hot water tank is to swap out the elements for mips and introducing the hot from the source horizontally into the tank at the top element hole and sucking supply form the bottom element hole. This stratifies the tank nicely and lets the hottest water go to the finishing tank and the coldest back to the heat source. It also allows some room for debris to fall to the bottom of the buffer tank which using the dip tube does not.

Can someone tell me what I am missing? I have recommend the element holes to a relative who is installing a dsh and would certainly want to know if there is a reason not to.

I believe that the element holes will give two to four time the efficiency of the dip tube method or am I wrong on something?

In most cases the tanks are very close to the heat source and the pumps move the water very quickly. GPM X DT = BTU's conveyed. Some manufacturers suggest throttling to increase DT, but that does not increase btus conveyed.

yes, the DSH usually only raises the temp by 5F, depending in the gpm which are going through it. The next time the tank volume is turned over, the temp is another 5F hotter. Just a matter of time until the water is heated up again. Yes, your point is a good one with the dip tube, however, we pump in the bottom, and out from the top, with the dip tube removed. Don't want to suck in any debris from the bottom.

It obviously works well as the monitoring reveals. Many ways lead to Rome….


http://welserver.com/WEL0713/

Thanks everyone for the replies and the discussion. Here are several more questions. 1. In the Bergy diagram what are the five circular symbols (3 in the supply line, 2 in the return)? 2. Since I have three desuperheaters are the pipe dimensions still ok (3/4" supply, 1/2" return)? 3. Is PVC or copper piping preferred? Thanks!

Copper, 3/4", those are ball valves

Posted By FBBP on 01 Feb 2014 10:20 PM
Bill et al. I am really confused by the continual honouring of this layout. It is only the geo industry that uses this. The solar and radiant industries go to great length to make sure a buffer tank stratifies yet the experts on this forum all seem to agree with this method.

If you go to Skyheating's wel server, you will see that his set up only raises the temp around 5 degrees. This is not even worth install the dsh let alone the buffer tank. If you spend a little time on the wel site reviewing some of the setups you will see that any tank set up this way produces very little energy. The one set up to take cold water from the bottom and sent the hot from the dsh to the top of the buffer produce lots.

Careful review of Skyheating's site will show that some of the hot water introduced at the bottom of the tank is sucked right back up the dip tube to re-feed the dsh. Any heat that escapes the dip tube suction works its way through the tank agitating all the water so that basically the whole tank is the same temperature.

The standard in the radiant and solar industries when using an electric hot water tank is to swap out the elements for mips and introducing the hot from the source horizontally into the tank at the top element hole and sucking supply form the bottom element hole. This stratifies the tank nicely and lets the hottest water go to the finishing tank and the coldest back to the heat source. It also allows some room for debris to fall to the bottom of the buffer tank which using the dip tube does not.

Can someone tell me what I am missing? I have recommend the element holes to a relative who is installing a dsh and would certainly want to know if there is a reason not to.

I believe that the element holes will give two to four time the efficiency of the dip tube method or am I wrong on something?

You need to have some background on my WEL to get the full picture, the customer of this WEL is very energy conscience so you will regularly see the buffer tank only a few degrees above incoming water temps and that is because this system is not used as often as most geo units. The customer usually lets his house have a big swing(sometimes as much as dropping to 62F and letting it raise up to 80F) so there is an 18 degree deadband in which the geo system does not run and does not produce domestic water assistance. In my house(no WEL or Geo currently, moving in 9 months and putting in geo in next home) I keep my house heated to 69 degrees and cooled to 73 so I get a lot more use out of my system. It also depends on what time of the day you look. I have looked at his WEL before they take a shower and the temp can get into the 80 degree range but keep in mind this system is the exception not the rule for geo. As of this posting its 34 degrees outside and 62 at the thermostat. This customer also runs the WEL themselves so I have no control over what values are input, the customer was nice enough to put my logo on in return for my company installing the WEL on our system for cost.

Bill et al. I am really confused by the continual honouring of this layout. It is only the geo industry that uses this. The solar and radiant industries go to great length to make sure a buffer tank stratifies yet the experts on this forum all seem to agree with this method.

FBBP,
If you look at how the water is moved, you can see stratification does take place. We draw water UP the dip tube and re-inject in the bottom. The volume of water moved is relatively small so large diameter pipe, or openings, are not required. This set-up is easy, quick and inexpensive.

Bergy

Thanks for the feed back guys. Lots of food for thought.
Doc - you say you have the dip tube removed. The diagram doesn't show that. That means you are reheating the hottest water and sending it back to the bottom, right? What stops the cold water from just flowing across the top when the is a DHW call?
One of the problems with my thinking is that I expected higher returns from the DSH. As you say, 5º per cycle. What would be the normal flow and head for a DSH pump be?

My thinking (maybe wrongly) is that the hottest possible water should be stacked up ready to go to the finishing heater. DHW is normally used a couple gallons at a time (except to fill a tub) so we are not really looking to get the whole tank hot, just the few gallons that are needed next. When you send the hottest water to the bottom, it has to work its way back to the top, so naturally the whole tank stays at roughly the same temperature rather then stratifying. So if I use a gallon to fill my tea pot and then 5 minutes later the dishwasher kicks in and draws two gallons and then someone washes their hands , etc., each time a few gallons of partially heated water flows to the finishing tank where it has to be finished off.

If the tank is fully stratified, each few gallons may well be at the finished temp before it enters the finishing tank even if the bottom of the buffer is only a few points above DCW temps.

Sky - yeah I finally got smart enough to realize that your client's geo is only running like 30 minutes a day. 'course Doc's is only running about thirty minutes too but then it runs for another 19 hours as well. Slightly more potential!! Doc - how does yours do in the shoulder seasons?

Bergy - you don't remove the dip tube, so completely different then Doc's, right? How does the water stratify when you both push and pull from inches apart at the bottom?

Joe - as you say GPM X DT = BTU's So the most efficient would be to draw the coldest water possible over the DSH right? Maybe it doesn't make much difference if the geo is running 19 hours per day, but at 20 minute per hour it might make a lot of difference, no? If we slow down the flow (smaller pump or throttle it down) we would not get more overall btus but with hotter output and stacking it near the outlet to the finishing tank, would we not get more efficiency out of the over all system? i,e, the electric elements would not have to do as much heating except at bath time? What is the hottest likely out put we would get from a DSH if it was slowed down?

Like I said, lots to think about.

"Joe - as you say GPM X DT = BTU's So the most efficient would be to draw the coldest water possible over the DSH right?"

I don't support drawing from the top as others do, but that's a different conversation. You are thinking of heat transfer being most efficient when DT is higher. While that is true, the capacity of the DSH is finite while with solar (as the sun may not shine for 19 hours a day) we need to harvest every btu possible in a shorter period of time. The sun's capacity obviously is much greater than a DSH and it can deliver btu's as fast as you collect (the DSH can not).

Every BTU you get from the geo system is used regardless of temperature. Every BTU used from DSH is one not created with resistance element. Drawing 1 or 2 gallons generally isn't going to activate your finish tank if replaced with warm water.

Posted By FBBP on 04 Feb 2014 11:41 PM

Doc - you say you have the dip tube removed. The diagram doesn't show that. That means you are reheating the hottest water and sending it back to the bottom, right? What stops the cold water from just flowing across the top when the is a DHW call?
One of the problems with my thinking is that I expected higher returns from the DSH. As you say, 5º per cycle. What would be the normal flow and head for a DSH pump be?

My thinking (maybe wrongly) is that the hottest possible water should be stacked up ready to go to the finishing heater. DHW is normally used a couple gallons at a time (except to fill a tub) so we are not really looking to get the whole tank hot, just the few gallons that are needed next. When you send the hottest water to the bottom, it has to work its way back to the top, so naturally the whole tank stays at roughly the same temperature rather then stratifying. So if I use a gallon to fill my tea pot and then 5 minutes later the dishwasher kicks in and draws two gallons and then someone washes their hands , etc., each time a few gallons of partially heated water flows to the finishing tank where it has to be finished off.

If the tank is fully stratified, each few gallons may well be at the finished temp before it enters the finishing tank even if the bottom of the buffer is only a few points above DCW temps.

Doc - how does yours do in the shoulder seasons?

http://welserver.com/WEL0713/
http://welserver.com/WEL0545/
You can see our setup here. When water gets drawn out, the cold incoming water is pull through the DSH first, putting it at the bottom of the tank. Plus the DSH will run very efficient, heating up 50F water in that case. WEL713 gives you an overview, but 545 details it a bit better. We found it important to put in a check valve, not to allow any back flow through the DSH. The controls ensure that as soon as water gets drawn out, the DSh is pumping. You can see by the temps and graphs how it is working.

I'm building a new home and plan on DIY geothermal with desuperheater (DSH) and a buffer tank with a heatpump water heater for the finish tank. Why couldn't I pipe the DSH suction from the buffer tank cold water line and pipe the DSH discharge to the buffer tank hot water line? I would install a check valve on the cold water line upstream of the DSH suction and remove any backflow preventer in the buffer tank cold water supply. I would verify the cold water dip tube is in place. This arrangement would allow the DSH to take suction from the buffer tank at the bottom of the dip tube (coldest water in the tank but above any sediment in the bottom of the tank) and provide the hottest water to the top of the tank for immediate use by the finish hot water tank if needed. Wouldn't this work or am I missing something here?

Doc - a few observations/comments.
I totally agree that that feeding the DSH the coldest water will be the most efficient. But for the purpose of discussion lets say that the DHW calls for an average of 5 minutes per hour. Does this mean that the DSH is getting the hottest possible water for 55 minutes? Also I don't understand how the 0713, part of the time shows the colder the water entering the DSH the colder the water leaving the DSH and then a goes through a period of the colder the entering water the HOTTER the leaving water???

So even if the geo is not running the DSH pump comes on when there is a DHW call effectively replacing the dip tube during a draw down?

Arkie - I was thinking along the same lines and I think it will work for low production situations.

The problem I see is that say it's a cold night and the geo has been pumping away and has the buffer tank nicely stratified, top is 130 and the bottom is 65-85. Arkie gets up in the morning and takes a shower. The DSH draws mostly DCW @ say 50º and heats it to 55 - 60º and sends it to the finishing tank while the water in the buffer tanks is still at 130º. Again it would work if the pump can be throttled down to the point that the leaving temps are around 80 - 90º or better.

At this point, I'm still thinking in and out of the element bungs is the way to go. The DSH always gets cold (if not the coldest) water and the leaving water will enter the tank about twelve inches down with minimal disturbance to the tank. If the water is hotter then what is above it, it will gently replace it. If it is colder, it will drop a bit but not disturb the bottom of the tank. The finishing tank always has access to the hottest water. Still think throttling the DSH is helpful or maybe a temperature controlled pump. I believe this is the most efficient overall but there is time when Doc's setup may feed hotter water to the finishing tank because he keeps reheating the hottest water. But it has to work its way up from the bottom, so maybe not??

Does anyone have a wel server that tracks DHW volumes and power consumption to show average cost of heating water? That would be most useful for this discussion.

FBBP, that makes sense.

So, it sounds like the best option is to get a hot water tank for the buffer tank that has upper and lower 1" threaded heater elements, remove those, and pipe the DSH supply to the lower element hole and pipe the DSH discharge to the upper element hole. That way, the DSH suction and discharge is mixed with the water in the buffer tank when there is a hot water demand and inrush of cold water into the buffer tank.

It looks like Rheem has already developed a thermal storage tank with the side taps replacing the heater elements here:

http://www.build.com/rheem-mts50200/s835343

They make these in 50, 85, and 105 gallon sizes.

Although, price wise, it would be much cheaper just to get a regular ~$400 electric tank type water heater like the one below and replace the heating elements with pipe nipples.

http://www.build.com/rheem-83vr52-2/s835289