2 questions:

1) Anyone know of a diagram explaining how a Desuperheater should be plumbed with a 2 tank system (unpowered buffer & NG both 50 gallon) ?

2) I've noticed something a little unusual with my Desuperheater/buffer tank and the water pressure coming into my house.  I have water hammering (just on the cold side) when the water pressure is unregulated  (I have a pressure valve right before the meters).  I can fix the water hammer by lowering the water pressure (quite a bit).

Here is the weird part.  When the water pressure is high the output of the buffer tank is warmer than when the water pressure is low.   I don't have a temp gauge for accurate measurements but I've noticed this over the last 2 months (heating season here in Maryland)

CH

Pipe the unit as shown in the drawing. Most manufactures require a delta T of 8~12 deg for the desuperheater.

Bergy

I've seen that diagram so often that it needs to be a sticky.

However, I'm not sure I agree that desuper needs 8-12 delta T. Mine works well with much less. I think it depends on the friction loss unique to each system - the geo mfg-supplied dsh circ pump does what it does against whatever combination of fittings and pipe runs to which it is connected - some (like mine) result in higher flow and low delta T ~5F, others may result in lower flow and higher delat T, ~15F.

Either way, it won't too much matter - DSH will grab some or all of the superheat off the compressor discharge and route it to the waiting buffer tank. So long as it is plumbed in rough compliance with the above diagram, it'll work well.

Compressor discharge hot gas is generally so much warmer than water in a buffer tank that good heat transfer will occur with a broad range of water flows.

My Christmas present is going to be adding a buffer tank and hooking up the desuperheater on my TTV038. I'm planning the plumbing required.... 2 questions.

1). Connection - I remember seeing this diagram before, but never noticed how the desuperheater "to" and "from" connections were shown. It appears to take water from the dip tube(cold connection)... and return it to the tank via the drain tap connection.

Does the water going out or coming into the dip tube come from a point in the tank below the drain tap point? How can I tell how far the dip tube goes down in my tank ? (bradford white standard 50 gal elec. medium height, dual element)

If the water discharged vai the dip tube is not below the drain tap, wouldn't it be better to pull the water (to be heated by the geo dsh) from the drain tap, and have it returned down the dip tube? (Opposite the connection shown in the diagram on this thread). That way you are ensuring you are pulling the coldest water in the tank for maximum amount of heating by the dsh..... I think I'm missing something.

With cold weather up here in West Michigan, comes long run times, so I'd like to get this piped soon to start generating some hot water.

2.) With all things being equal, the climatemaster catalog (TTV038) shows higher DSH capacity in heating mode rather than cooling mode? This really isn't an issue as I only run cooling for max 2-3 weeks a year, but it sounds counter-intuitive ( in cooling mode there should be lots of heat to reject to some cool domestic water, right?). Any ideas??

Thanks!

If you haven't already, you might want to read the thread on Justifying 2 Electric Water Heaters. While a buffer tank will get 100% of the benefit from the desuperheaters, I am one of a handful of homeowners that have stated on this forum that they are very happy with the results from the single electric tank setup that they have.

Back to your question:

1) I believe that drawing water from the bottom drain tap could result in more sediment from the water tank being drawn into the desuperheater (compared to drawing from the dip tube) because heavier particles will settle to the bottom of the tank. This could result in clogging of the desuperheater. Not positive, but I think the dip tube goes about 2/3 of the way down the tank. Since most of the activity is still happening at the bottom of the tank, I assume the benefits of drawing from the dip tube outweigh the possible problems that can result from drawing through the bottom drain.

I'll leave #2 to someone better suited to answer this question.  I can say that we leave our DSH on all the time, but our Envision unit is supposed to not turn on the DSH if conditions aren't right for contributing to hot water production.  I don't know if your model has a similar feature or not.

While everything is apart (and if possible) I would install a 3/4" full port 1/4 turn ball valve with a hose bib on the end (about $7.00 at Lowes). This will allow larger pieces of sediment to be flushed out (compared to a drain valve) when you do periodic tank flushing.  Make sure you have room to turn the handle. 

Geome,

I have read the "justifying 2 water heaters" thread with great interest !! And see your point larger single tank can work, as well as the others point dual tank is good for most. For myself we already have a 50 gal elect, with a larger household, sporadic heavy usage throughout the day and night, we wouldn't have enough hot water if the bottom element was turned down.... AND some day I intend to connect my basement infloor heat to the domestic water (directly or indirectly), so the additional 50 gallons provided by the buffer tank will give me some more "flywheel effect".
Great tip... about replacing the drain valve with full port ball valve.

All...
Can someone confirm the sediment issue as the reason for piping it as shown in the diagram ??

Also, I'm wondering why plumbers don't put the tanks on blocks or a stand.... the drain port is about 1/2" from the floor and almost impossible to work on or connect to ! Is there a code issue with not having them flat on the floor ??

Thanks!

If I had high hot water usage, and receive occasional overnight guests, and have enough electric capacity, I would power the buffer tank and leave the circuit breaker off. When guests arrive, I would switch the breaker on to provide additional hot water capacity, but remember to turn it off when they leave. I can't take credit for this tip. Heard it from a pro.

Don't forget the drain pan(s).

That is a good idea. I'd have to weight the benefit against the cost of another #10 wire from the panel across the house to the tanks.

Also, you have to be careful, you make it too comfortable and the out of town guests might never go home !

Yep. I make the in-laws shower last.

Sediment is the reason we pull water up through the dip tube. If you have a demand that exceeds your 50 gal. tank you should consider an 80 gal. tank. The desuperheater only runs when there is a call for heating or cooling. The spring and fall do not provide a lot of domestic hot water.

DO NOT hook your radiant load to the domestic water heaters!! There are BUGS you do not want your family to come into contact with in the radiant tubes. It is better, and more efficient, to have a SEPARATE heat source for the radiant.

Bergy

I would never pull dsh water from boiler drain - sediment is best left at the bottom of the tank, not drawn into heat exchangers and pumps.

As to this question:

2.) With all things being equal, the climatemaster catalog (TTV038) shows higher DSH capacity in heating mode rather than cooling mode? This really isn't an issue as I only run cooling for max 2-3 weeks a year, but it sounds counter-intuitive ( in cooling mode there should be lots of heat to reject to some cool domestic water, right?). Any ideas??

I realize this seems counter-intuitive but there is more heat available in heating mode for water since the system runs at higher refrigerant head pressures and temperatures during heating season. Understand that in heating mode heat diverted to water is then not available to heat air - robbing Peter to pay Paul, but it is still a cheap way to heat water in all but the coldest weather.

In cooling mode the object is to reject heat, so any heat that goes to water is nearly pure 'gravy' (nearly free) but that heat tends to be available at lower temperatures, so less of it makes its way into the water.


Hope that helps...

Engineer/Bergy/Geome - Thanks for the replies. Pulling from the dip tube rather than the drain connection makes perfect sense now. In-experience is speaking here, but what do you think about returning water from the dsh to the tank via the hot connection or T&P connection so that I can provide coldest water to the dsh rather than mixed conditions ???

Bergy - Radiant Direct (online) has documentation showing how infloor heat can be connected to domestic system and meet some/all? state plumibing codes. I haven't looked at it in a year or more, but that was the thought in the back of my mind. The benefits appeared to be: less upfront cost (one water to water heat pump to heat domestic and infloor heat, no heat exchanger required, one less circulation pump), quicker heat transfer from source to floor (no heat exchanger), less space required in mechanical room. The upfront cost was/is the big kicker for me, why I haven't done anything on it and am still exploring all options...

In-experience is speaking again... :), but why is separate equipment better or more efficient ? Initialy I thought you were getting at redundancy, but if the systems (infloor and domestic) aren't tied together, redundance is not a factor....

I would think that returning DSH water to the top of the tank may tend to cool off the hottest water in the tank if the water drawn in to the DSH from the dip tube is significantly colder than the water at the top of the tank. The DSH only heats the water 5-15 degrees each time through. Best to keep the hottest water at the top of the tank to be either used directly in a 1 tank setup or sent to the water heater in a 2 tank setup.

jokin,

Most codes only allow domestic and radiant water if there is a heat exchanger, keeping the two from mixing...unless the heat exchanger leaks. Do you want your family drinking water that has been stagnate and growing all kinds of bugs?  If a heat exchanger is used, not all of the energy is transferred from the source side to the load side. If your heat pump is making 110 deg. water, about 100 deg. water will go into the tank. ( A loss of efficiency.)

Remember... There are a LOT of hack operations on the internet. They will say ANYTHING to get you to send them the money. Once you own the product, good luck getting Mr. Internet to call you back should problems arise. Case in point. We have a client who ordered a condensing unit for a cooler off the net. We installed it for him and less than a year later the compressor failed. Mr. internet refused to warranty ANYTHING so our client's initial savings of $500.00 was gone, plus he had to buy another unit from us.

Do your family a favor...DO NOT even consider combining domestic and radiant!! Be smart...be safe.

Bergy

Thanks for the tips Bergy!

Don't worry I refuse to buy equipment on-line. That's crazy.

As for the heat exchanger, I understand completely the issue with the heat exchanger efficiiency penalty, because the production side of the heat exchanger most be higher temperature than the load side (what you acutally use in the floor). Warmer water means reduced geo efficiency.

I agree totally about danger of piping them together (water stagnation and BAD bugs), however, the above efficiency impact of a heat exchanger and the upfront cost of having separate heating equipment for domestic and infloor has kept my eyes open to options. I haven't looked at it recently but from what I remember the pipng arrangement ensured that every time hot water was used in the house it went through the infloor heat pipes... this is how they claimed to avoid problems related to stagnation. What I don't remember is how they ensure that all zones are being "flushed", and not just the one with the least pressure drop, etc? So I'm not convinced its even possible... just still curious. When I think I might actually be ready to do something and get some time I will try to dig this up again and take a closer look... and post here if I have questions.

Thanks for the well informed responses !

You really don't want to mix the domestic hot water system with the heating system.

1.) The temperature needed by an water coil air handler or a  floor system is ~100F. Not hot enough for DHW w/o some equipment for topping up the temperature ie a hot water heater anyway. GSHPs can make 100F nicely, anything much higher is hard on equipment and at a loss in COP=$$$.
2.) Introducing fresh make-up water into a hydronic loop is a guaranteed recipe for loss in efficiency from scaling of the in-floor tubing, coax exchangers and pump/fitting corrosion, all from the dissolved oxygen, DO in the make-up water. As a closed loop the DO is soon depleted,  leaving a  clean  heat transfer fluid  for  the  intended purpose.

Most GSHPs offer an accessory desuperheater, DSH for reclaiming a part of the heat generated by the refrigerant cycle  that can be diverted  to  DHW. The exchanger for this purpose is designed to be cleaned to remove the above mentioned scale on a regular basis.

Consider including a DSH in your plans or a separate Heat Pump Water Heater for low operating cost hot water generation.

Dick

Pipe it per Bergy's diagram.

Bergy, it would be useful if your diagram depicted dip tubes, at least the one in the buffer tank so folks could better understand the flow paths and the importance of letting natural stratification take its course with minimal disruption by hot water use and dsh circulation.

Done...

Let me reiterate, that diagram needs to be a sticky or made similarly easily available - the last word in dual tank DSH plumbing