I second that "NO", you can ruin your circulator pump.

Climatemaster now has a new circuit board, and guess what, a whole circuit board only for DSH function! There are now dip switches for 125 or 150 degree setting. And a dip switch to activate/deactivate the DSH pump. Oddly enough, when the dip switch is in the off position, the DSH pump is activated.
Anyway, they monitor the entering load temperature and the compressor discharge temperature, and the board will allow the pump to run if the delta is 14 degrees F or higher. Above 128F DSH ELT temperature, they add 0.2 degrees to the 14 degrees required delta per degree above the 128 F. So the hotter the DSH gets, the higher the required delta is.

That way they allow DSH running at lower temperatures. One more reason for a buffer tank. The change has been made in units made after JULY 2010.

Posted By docjenser on 11 Nov 2010 09:55 AM
Oddly enough, when the dip switch is in the off position, the DSH pump is activated.

Maybe it's a "DSH Off" dip switch?  So, off=not off=on, and on=off. 

Yeah, I could not follow that logic either

OK so don’t touch the DSH ball valves. But no issues with using solar tank as DSH buffer tank?

Thanks, john

There is no risk. Your DSH pump will simply not turn on if the solar tank is already too hot......The Europeans do it like that all the time.

Is the buffer tank rated to withstand the solar water temperatures?

Yes. It's actually a Solar tank/heat exchanger that I would like to also use as a buffer tank for the DSH. The Solar tank is rated for 185 Degrees.

The german version of the stiebel-eltron installation manual actually displays exactly this scenario. No forced air units there, all hydronic, so they would lack hot water generation in the summer unless there is a year around hot water setup. So they use solar hot water for the shoulder season and in the summer. I see if I can dig it up and post it as an attachment.

I thought I would provide a follow up to this thread. Over the weekend we finally moved the DSH water pipes from my 80g electric water heater to the 80g solar/buffer tank. So far it seems to be running well.

After the first night the tank was warmed to ~75 degrees. Last night ~90 degrees. Very happy with the results considering the amount of hot water we use (4 adults). I also reduced the length of the pex running between the DSH and buffer tank by ~15-20 feet and completly insulated copper/pex. This pretty much eliminated the heat loss I observed between the DSH and buffer tank!

I have noticed one issue. The bottom of the buffer tank is connected to the DSH input port and the DSH output port is connected via tee to the cold water inlet on the buffer tank. In the morning when we start taking showers I noticed the EWT to the DSH reached 100 degrees. This should not be possible since the water at the bottom of the buffer tank was nowhere near 100 degrees.
Looking at all the temp sensors I discovered cold water entering the buffer tank while someone was taking a shower was taking two paths. One path directly into the buffer tank and the other via the DSH lines. The high EWT temp on the DSH input was caused by the cold water pushing water in the reverse direction in the DSH lines.

I followed the CM installation instructions for DSH with a buffer tank and there was no mention of a check valve requirement. Should we have installed a check valve on the DSH out line near the buffer tank to prevent the reverse flow of water through the DSH lines?

http://welserver.com/WEL0167/

John

Posted By jpespisa on 15 Dec 2010 01:24 PM
I thought I would provide a follow up to this thread. Over the weekend we finally moved the DSH water pipes from my 80g electric water heater to the 80g solar/buffer tank. So far it seems to be running well.

After the first night the tank was warmed to ~75 degrees. Last night ~90 degrees. Very happy with the results considering the amount of hot water we use (4 adults). I also reduced the length of the pex running between the DSH and buffer tank by ~15-20 feet and completly insulated copper/pex. This pretty much eliminated the heat loss I observed between the DSH and buffer tank!

I have noticed one issue. The bottom of the buffer tank is connected to the DSH input port and the DSH output port is connected via tee to the cold water inlet on the buffer tank. In the morning when we start taking showers I noticed the EWT to the DSH reached 100 degrees. This should not be possible since the water at the bottom of the buffer tank was nowhere near 100 degrees.
Looking at all the temp sensors I discovered cold water entering the buffer tank while someone was taking a shower was taking two paths. One path directly into the buffer tank and the other via the DSH lines. The high EWT temp on the DSH input was caused by the cold water pushing water in the reverse direction in the DSH lines.

I followed the CM installation instructions for DSH with a buffer tank and there was no mention of a check valve requirement. Should we have installed a check valve on the DSH out line near the buffer tank to prevent the reverse flow of water through the DSH lines?

http://welserver.com/WEL0167/

John

Yep, in my experience a checkvalve is a must, but also between the buffer tank and the final make up tank. It significantly improves performance. We test run it with or without it. You have thermal siphoning without it, decreasing performance quite significantly and cooling down your water by entering the lines. Even if you insulate the lines, it will not do the trick.

Interesting, I hadn't thought of the thermal siphoning issue between tanks. Thanks for the tip!

Posted By jpespisa on 15 Dec 2010 09:02 PM
Interesting, I hadn't thought of the thermal siphoning issue between tanks. Thanks for the tip!

You should have a checkvalve in the line from the buffer tank to the make up tank. The second check valve needs to go after the T in the return line to the DSH of the heatpump.

The checkvalve for the DSH line. Is it critical where we cut it in? I was planning on installing the check valve just before the tee on the buffer tank cold water inlet (DSH out line). We installed a 9” horizontal length of copper from the Tee just in case we needed to cut in a checkvalve. If it’s better to place the check valve on the DSH in line then that’s where we’ll install the it.

DSH out
|                   |
|                   |
| ------CV-------| Tee 
                     | 
                     | Cold water inlet 
            ------ |------ 
            |                | Buffer Tank 
            |                |

Thanks, John

Posted By jpespisa on 16 Dec 2010 10:56 AM
The checkvalve for the DSH line. Is it critical where we cut it in? I was planning on installing the check valve just before the tee on the buffer tank cold water inlet (DSH out line). We installed a 9” horizontal length of copper from the Tee just in case we needed to cut in a checkvalve. If it’s better to place the check valve on the DSH in line then that’s where we’ll install the it.

DSH out
|                   |
|                   |
| ------CV-------| Tee 
                     | 
                     | Cold water inlet 
            ------ |------ 
            |                | Buffer Tank 
            |                |

Thanks, John

Yep, after the T in the cold water inlet line, in the horizontal portion towards the DSH in at the heatpump.