Hello All,

My company is building a new facility.  We have a two story office space totaling about 2500 sq ft.  We are installing a 2 stage Geocomfort Geothermal system in the 2-3 ton range for each floor.  The units will come with the DSH option and I've been scouring the forums on how to handle this.  Most of what I've researched is really for homes with moderate to heavy hot water demands.  We will not have those type of residential demands.  Although we will have a shower that is something that might get used at a max 1 day a week and general hot water for hand washing and possibly washing down boats. 

The contractor has said all we need is a gas or electric hotwater heater and the DSH will work fine.  Well, I've discovered that I should likely go electric vs. gas and I see most pro's on this and other forums suggest two tanks.  I'm thinking this would be for residential with higher demands?  Anyway, my question is what is the optimal setup for this, will a 30- 40 gal tank work and are there any diagrams that someone could share for a setup / use like this. 

Thanks so much!
Chris

I see the attraction in your mind - matching a small (cheap to operate) hot water source to a small hot water load. However, DSH delivers only when the unit runs for heating and cooling - some days you'd have a full tank of hot water ready to go, some days not.

Using hot water to wash boats will empty a tank quick. I take a 10 minute shower but I'ver never washed a boat that quickly.

In your shoes I would not have ordered the DSH option. Your described light and intermittent hot water use will, IMO, never allow the savings to pay back the investment.

I agree, most commercial applications do not justify the added expenses. On the other hand, now that you have it, get a buffer tank, pipe the DSH into it, and use whatever preheat you can get out of it. Then finish off with either a second electric or gas tank so you have hot water all year around. That way you at least preheat most of the time. You can debate wether it is worth it to pipe in the Heat Pump, I don't know how far away it is located from the tank(s).

Thanks E,

I should clarify a bit.  I got the DSH's on the system for free since I was competing a Bosch FHP with the Geocomfort, so the extra cost was not an issue.  BTW, it is still not to late probably to get them not installed.  Also, I do recognize I need an electric water heater regardless, so not trying to get away with just a storage tank.  I need probably 40 gal (for the reasons you mentioned) but getting my friend in the biz to price a 50 gal shorty Marathon.  I guess my question is in this application (not too much hot water, and certainly doesn't matter if I run out washing a boat) do I need the two tanks. 

The contractor tells me that a single tank will work fine but I'm not convinced from your previous threads.  Just see that my application is much different than a residential so wondering what the ideal setup would be here.

Thanks so much I really appreciate it!
Chris   

I agree with DJ if the order for the DSH option cannot be cancelled now.

Thanks Doc,

All the equipment, including the compressors, water heater (potential buffer) and softening is all right under a set of stairs.  The water runs are fairly short as well.  For example I would think the upstairs kitchen and shower (again all low use since commercial) is probably less than 20'.  So you vote buffer tank.  hmmm.  Thought this might be a cut and dry one. 

PS. I've really enjoyed reading all your alls posts.  Fascinating.  My company does high-resolution seafloor mapping so all the monitoring equipment you are working with is really cool.  Since we are an environmental type company we have been trying to do as many "green" elements as possible. 

Thanks guys and any other info I can provide to help with this problem let me know.  I really appreciate it!
Chris 

So E. You think I should maybe just cancel the DSH option? I have seen this might use more power? I guess this leads to maybe a bigger question (and feel free to no answer and open up the flood gates) but should I have then gone with the FHP vs. GeoComfort? Also, I orginally thought and planned on putting in an on demand type water heating system. wondering if I have just confused the whole situation.

I guess the obvious question is what benefits would I see by just piping the DSH directly into a 30-50 gal electric HWH?

Posted By FreeNC on 07 Feb 2011 02:18 PM
I guess the obvious question is what benefits would I see by just piping the DSH directly into a 30-50 gal electric HWH?

Almost none, the DSH would compete with the electric heat elements. It will hardly turn on.
http://welserver.com/WEL0288/
Here is a WEL with a 50 gallon buffer tank and a on demand hot water heater after that. That way you capture all the heat you can get from the DSH, and always have all the hot water you will need. Works well! (don't pay too much attention to the indoor temp, it is a weekend home they keep at 60 F during the week).

Thanks Doc,

I'm going to check your setup today or tomorrow. I appreciate the help. Juggling a bunch with the build so had to put the water heater to DSH down for a day or so but I'm thankful you guys are here to help.
Chris

PS. Doc.

I'm a little unclear on "almost none, the DSH would compete with the electric heat elements. it would hardly turn on" Isn't that what I'm after. To heat the water in the tank from the DSH so that the elements wont come on as much to save money? What power the elements use is to just get the water to the desired temp? Clearly I'm a newbie to all this so excuse any ignorance I have. Just trying to use as little E in this setup. I was also considering putting a timer on the electric (since I'm now convinced that gas will not be as efficient) HWH since we won't want to heat at night and on weekends. Any suggestions on timers or if this is even a good idea? I have yet to come across a digital timer that could do weekends but again I'm just getting into this.

Thanks Doc and Engineer!
Chris

I meant the DSH would hardly turn on,better said the pump to circulate water through the DSH, because your electric heat elements would bring the tank quickly up to the setpoint temperature after usage. In a 1 tank set up the electric elements compete with the DSH, but since they have much more capacity, most of your hot water will be made with electric resistance. With a buffer tank, you disconnect those competing heatsources, so the heatpump has much more time to raise the water temperature after usage. In addition, the heat capacity in the summer will be more limited. So it might do a great job to heat your water from 50-90 F, but not much higher. But if the water is not cold but already hot via the electric heat, the DSH will not turn on. So in the summer it might only preheat with 2 tanks, and not turn on at all with 1 tank setup. The reason for that is that in AC mode the DSH needs higher loop temperatures, which it does not always reach. It is an inherent problem with R-410a freon. The only way to capture any heat heat is to use a buffer tank with colder water. If you use a foam insulated tank, the heatloss will be minimal, not much need for a timer setup.

Thanks Doc,

I see where you are coming from.  Your explanation is crystal clear.  Attached are the two setups my contractor can use. He did mention this morning that the DSH is always "on" (but you can switch totally off if desired) and doesn't necessarily have a thermostat type function where it would only cut on if the water is at a certain temp?  Dunno.  I am going to look into this much more later today but your explanation makes complete sense if my DSH would in fact compete with the electric HWH.  Will update.  Thanks again everyone for helping me out.  

Sorry about the edits.  hope you guys didn't get a bunch of notices.  here is the single tank setup.  

Posted By FreeNC on 10 Feb 2011 11:24 AM
Thanks Doc,

I see where you are coming from.  Your explanation is crystal clear.  Attached are the two setups my contractor can use. He did mention this morning that the DSH is always "on" (but you can switch totally off if desired) and doesn't necessarily have a thermostat type function where it would only cut on if the water is at a certain temp?  Dunno.  I am going to look into this much more later today but your explanation makes complete sense if my DSH would in fact compete with the electric HWH.  Will update.  Thanks again everyone for helping me out.  

Yep, that is the setup. The DSH is alway on, you cannot disengage it, what is turned on and off by the circuit board is the circulation pump which pumps water from the DSH into your tank, and on some units you can shut that pump off manually. Below you can see the R-410a issue. Climatemaster and Waterfurnce now have similar logistic controls for the DSH, namely compressor discharge temperature (=DSH temperature) muts be at least 35 degrees above incoming water temperature from the tank (=tank temperature). If your tank is heated by an electric element and at 125 F, this DSH pump will never turn on in the summer. The only way to get it to turn on is to feed it with colder water, like 50-100 degrees from a buffer tank, to reach that 35F differential. Your installer might not realize this. It is the same issue for all geo heat pumps, inherent with R-410a. Now, Geocomfort is a Hydron clone, I have to look up what their control logic is.

Waterfurnace Envision install manual: "Note: Under certain conditions, Envision dual capacity units operate with very low refrigerant discharge temperatures, producing little or no water heating capability. This scenario occurs when the unit is operating with cold entering source water (loop or well). Allowing the hot water generator pump to operate during these conditions actually removes heat from the DHW circulating through the unit. To overcome this, Envision unit microprocessors have been programmed to disengage the hot water generator pump during such conditions. (During low capacity cooling operation, the pump will operate only if the DHW temperature entering the unit is less than the liquid line temperature plus 35° F. During high capacity cooling operation, the pump will operate only if the DHW temperature is less than the liquid line temperature plus 60° F.) Using a preheat tank, as shown in Figure 12, will maximize hot water generator capabilities."

Thanks Doc. This info is amazing. I appreciate it. The geocomfort system we are getting is 2 stage but I do not know the model number. If that is important I can get it.

Chris

The single tank diagram is doable but does little actual water heating per Doc's explanation

Posted By FreeNC on 10 Feb 2011 12:49 PM
Thanks Doc. This info is amazing. I appreciate it. The geocomfort system we are getting is 2 stage but I do not know the model number. If that is important I can get it.

Chris

The problem is the same for every DSH setup, there just seems to be a different approach to deal with it.

Hydron install manual:

"Hot Water Pump Control Controls for high water temperature and low compressor discharge line temperature prevent the hot water (desuperheater) pump from operating when the leaving water temperature is above 130°F, or when the compressor discharge line is too cool to provide adequate water heating."

It appears to me that they do not monitor the compressor discharge AND the incoming water temp, but simply shut off the circulation pump when the loop is not warm enough, which was the older and very inefficient way CM and WF did it the last 2 years after the problem surfaced. But may be there is something I do not know or which they do not tell you, and they have a better way to control this. Issue is always the same, no matter what model number or manufacturer. DSH pump will not run in A/C mode if the outside loop does not have a minimum temperature which results in a compressor discharge temperature over 125 F (Hydron, Geocomfort) or if compressor discharge Temperature is below 125F, it needs to be at least 35F higher then the entering DSH temp (CM, WF with their new logic boards). Unless Geocomfort has changed that logic control, your DSH will not engage in AC mode when your loops are too cold.