Would need the lower element on during shoulder months in a single tank setup. Yes, manual intervention is required with a single tank setup, but a buffer tank is more "plug and play" or rather "no plug" and play. I understand why installers like this method, but our setup still works very well for us. I don't mind the minimal interaction, or maybe I just like going downstairs to see the blinking green lights.

"While I agree with that analysis, it basically mandates a buffer tank. Turning off the lower element is simply not an option in nearly all instances. Doing so deprives the home of about 75% of the total capacity of the water heater. In times of no DSH production a 60 gallon water heater with no lower element would have only the top 15 or so gallons warm, barely enough for a single short shower. Few families would abide that situation."

Same is true for a gas-fired HWH.  The equivalent to turning off the electric element is turning down the gas-fired HWH's tstat low enough to keep the HWH's hot water output temperature below the ever cooling (as the cooling season winds down) compressor refrigerant discharge temperature.  Makes for pretty tepid showers if you're insistent on making the DSH work properly with a direct-connected gas-fired HWH.

I have a nice chart that illustrates all of this, but, I think the days of any remaining cooling needs are almost over here in the Dallas area, so it doesn't show anything at the moment, unfortuantely ( http://www.welserver.com/cgi-bin/pl...rPerf2.gif ).

Best regards,

Bill

Thanks for the response WF.
I will resist the urge to paraphrase.

Can we expect to see the no buffer DSH configuration removed from your installation instructions soon?
Why have someone pay for a DSH and then recommend an installation practice that minimizes results/benefit?
Kudo's for the extra temp sensor.

For those running a DSH on a R 410 system with no buffer and no DHW temp sensor, your results will go from minimal benefit to measurable loss (i.e. 2 year old TT27 such as my cited customer).


j

Please don't take this in a confrontational way, it's not meant as such. Manufacturers may be interested as well since they are being asked to change their installation recommendations.

Installers that have installed single tank DSH systems: What percentage (and approximate number) of single tank setups have you had to change to dual tank setups due to the single tank DSH system not contributing to hot water production? I'm not talking about call backs, just changes from a 1 to 2 tank setup. How many that you changed to dual tank systems have had data supporting the problem? We know of 1 instance with Joe. Please specify the number of electric vs gas single tank systems changed to a dual tank setup.

As you all know, the best thing we can do for our customers is to give them the information and explain their options, then let them decide what is best for their application.  WaterFurnace will continue to provide information on single and dual tank installations.

The decision to use one tank or two should be based upon the homeowners DHW requirements.  We understand that a single tank has limited storage capacity.  If this is not enough you should install the second tank.

WaterFurnace International, Inc.

I had two single tank installs where the owners wanted to save the money. One owner was not happy about the quantity of hot water and the recovery time, and we installed a buffer tank, problem solved.
Second one is a single person household, only takes showers, he is fine with it but does not realize that the DSH competes with the electric heat elements, shuts off too early, and especially in the summer time does not contribute at all since the tank is already too warm and DSH output is limited, if not completely diminished.
After I have seen the performance with a single tank setup, I either don't put them in at all, or install a 2 tank configuration. Our reputation is on the line, customer is not completely happy, and I have to run out and fix things. I just hate it when a customer goes around and says "Geosystem heats fine, but there are issues with not enough hot water....".
Geo would have a much higher installation rate if people were not uncertain and would not question if it is up to the task of completely replacing a conventional system. Their expectations are very high, rightfully so, given the increased amount customers have to pay for an install. One issue with a geosystem is one issue too much. Look at all the complaints with DHW on this forum, pretty much all came from installs with one tank.
Never had a single complaint with 2 tank setup. You guys at WF should think about it, namely that sub-optimal system designs, even if elected by the customer, are counterproductive in having a higher acceptance rate for geosystems.

Thanks Doc. If our system didn't work well (but it does), I'd be first in line to complain. With EWT's factoring in to the equation, would closed horizontal loops be more or less inclined to have problems with a single tank system in cooling mode compared to closed vertical loops? How about region, or combination of region and loop type? Our installer has been in geo for 10+ years (I believe), and he doesn't have the problems with single tank setups, or he wouldn't recommend them either. There must be reasons why some units work well with a single tank and some do not (even in cooling mode.)

They work especially poor in A/C mode when the loop is cold, so heat dominated climate is not great. Run time is also important, the shorter the cycles the poorer the performance. Even the buffer tank never got above 90 degrees F here in the summer. If there would have been only one tank, set at 100 degrees minimum for DHW, not to drop below lets say 100 degrees, the DSH would have never turned on. With two tanks, at least it heated it up at least from 50 to 90 degrees.
Geome, how do you know that the heat in your 1 tank configuration is coming from the DSH, and not mainly from your electric heat elements?

Our DSH always runs when the geothermal system runs and the DSH Out is always hotter than DSH In. Our water heater timer also limits the elements from running until just before predictable hot water usage (to top off the hot water if the DSH hasn't.) Our big tank for our relatively small hot water usage helps.

Geome you asked about gas water heaters with 1 tank, does WF permit this installation? I know of no other manufacturer that does.

Your combination of timer interupting elements and the DHW temp sensor provided by WF combined with large storage and low requirements works, but little else would.

As I mentioned before, in the absence of the DHW sensor little else would work.

I maintain that there are lots of 1 tankers out there that are unaware they are paying extra, as they expected an electric bill jump when system was installed.

Joe

joe.ami,

You are correct. WaterFurnace does not recommend using gas water heaters with a 1 tank installation.

WaterFurnace International, Inc.

Interesting thread. One post earlier answered most of my questions. I was kind of beffuddled why so many single tank desuperheaters don't produce. Because mine has been awesome. Too much so sometimes. I'm getting ready to add a mixing valve above my HWH to cool of the water to the house. I have an older DX system (r22) that I updated the desuper heater on the single tank system about a year ago. It is piped like the Original posters. Cold out from bottom of tank returned to tank via hot on top. Mine maintains 130+ degrees in the HWH with the breakers turned off anytime the system is running. I've been known to go for weeks on end without electric to the HWH. I intend to install a buffer tank by next summer just to store more hot water. That way during seasons where my system is not running regularly such as spring and fall I can leave the breakers off. With just 2 of us using water 100 gallons should last for several days. I hate having to kick on the electric to heat cold water because the geo has been off for a couple of days in nice weather.

R 22 has higher discharge temperatures out of the compressor and that's what heats the water. It's a trade-off.... with R 410A you get better efficiency.

As long as the breakers are off a single tank system acts like a two tank system. Once the breakers are back on, the relatively quick recovery of the heating elements leaves the desuperheater with nothing to heat 90% of the time.

Note that with a second tank you'll have a bit more standby loss. A well-insulated tank might lose 5-10 degrees per day

As I mentioned earlier in this thread I am planning on reducing the length of PEX from my DSH to the hot water heater. I’m now reconsidering using my solar water tank as a buffer tank for the DSH.

The solar water tank/heat exchanger looks and is plumbed like a 80 Gallon Electric water heater. It has two additional connections for the glycol to circulate through a heat exchanger loop wrapped around the bottom of the tank.
Since the solar tank is already acting as a buffer tank for my water heater, it would be fairly simple to connect the DSH to the solar tank.

The concern I have is the water in the solar tank can reach 150 degrees during the summer months. My DSH rarely turns on in the summer, so I think the risk of hot water reaching the DSH is pretty low.

Has anyone tried this configuration? Is this a bad idea?

Thanks, John

http://welserver.com/WEL0167/

We have a different setup, but a few things come to mind.

With our Envision system, there is a high limit temperature sensor on the DSH. From our owner's manual:
"A safety device (sensor) shuts off the circulator for the desuperheater in the event that the water temperature reaches 130° F (54° C)."
If your unit has a similar function, maybe this is all that is needed?

Our unit also has a switch on the door of the unit to manually shut off the DSH. I wonder if other manufacturers have dip switches that a qualified person can use to manually turn off the DSH?

Only if the DSH is manually switched off, you could use some ball valves to make sure nothing flows to the DSH.  I don't know if the valves are necessary.

The Climate Master model (TT 27) I have will shut off the DSH at 125 Degree's. I was hoping this would be enough protection for the DSH. Unfortunately I have never found any documentation regarding an on/off switch for the DSH.

Is it safe to shut the ball values? I didn’t want to take a chance of damaging the DSH pump if no water is allowed to circulate.

John

Posted By jpespisa on 10 Nov 2010 02:12 PM
Is it safe to shut the ball values? I didn’t want to take a chance of damaging the DSH pump if no water is allowed to circulate.

You have a different system than ours.  For our system:

"A switch located below the status lights, enables you to manually turn off the internal desuperheater pump. When this switch is off, your unit’s hot water pump is manually disabled, and DHW OFF status light will be lit. This switch may be used when the water heater is being serviced or replaced. This switch must be turned off when water flow from the water heater to the unit is turned off or disconnected. Damage to the pump may otherwise occur."

Sounds like the DSH pump can be damaged if valve(s) are shut and the DSH pump is energized.

Installers here should be able to tell you if it is safe to rely on the cutoff sensor to protect the DSH system (or if you would need to do more.)

P.S.  Always best to involve your installer so as not to void warranties, etc.  They should know your system/setup better than anyone.  :-)

Posted By joe.ami on 11 Nov 2010 09:29 AM

...This is why as an installer, I put a t&p valve on my dsh circuits and as an inspector I ask others to do the same.

Sounds like a great idea.  Would you tell us what you use?  Is this typically manufacturer's installation instructions?

I'll remove the handles to our DSH ball valves today to keep an unsupervised child (or unsupervised father-in-law ) from easily turning the handle.  I'll keep the handles nearby, but out of sight.