Desuperheaters in series - GreenBuildingTalk - GreenBuildingTalk - Green Building Forums on Insulating Concrete Forms (ICF), Structural Insulated Panels (SIP), Radiant Heating, Geothermal Heat Pumps, Solar Power, Green Construction Projects - Green Building Technologies

Forums

Unanswered Active Topics

Forums Search Members

Forums > Green Building Technologies > Geothermal Heat Pumps

Desuperheaters in series

Last Post 11 Feb 2014 11:09 AM by FBBP. 27 Replies.

Sort:

Prev Next

You are not authorized to post a reply.

Page 2 of 2

Author

Messages

arkie6

Veteran Member

Posts:1453

08 Feb 2014 06:38 PM
As usual, nothing is as simple as it seems. It turns out that screw-in water heater elements use a 1" NPS (straight) thread whereas pipe nipples and pipe reducing bushing use NPT (taper) threads. This is why the water heater elements use a rubber gasket to provide a water tight seal. I searched for a 1" NPS male to 1/2" or 3/4" NPT female reducing bushing, but found nothing. I'm sure someone out there makes an adapter for this application, but I haven't been able to find one.

FBBP

Veteran Member

Posts:1215

08 Feb 2014 07:39 PM
Posted By arkie6 on 08 Feb 2014 06:38 PM As usual, nothing is as simple as it seems. It turns out that screw-in water heater elements use a 1" NPS (straight) thread whereas pipe nipples and pipe reducing bushing use NPT (taper) threads. This is why the water heater elements use a rubber gasket to provide a water tight seal. I searched for a 1" NPS male to 1/2" or 3/4" NPT female reducing bushing, but found nothing. I'm sure someone out there makes an adapter for this application, but I haven't been able to find one. arkie - I just used a standard pipe nipple and it worked fine.

FBBP

Veteran Member

Posts:1215

08 Feb 2014 07:49 PM
Posted By FBBP on 08 Feb 2014 07:39 PM Posted By arkie6 on 08 Feb 2014 06:38 PM As usual, nothing is as simple as it seems. It turns out that screw-in water heater elements use a 1" NPS (straight) thread whereas pipe nipples and pipe reducing bushing use NPT (taper) threads. This is why the water heater elements use a rubber gasket to provide a water tight seal. I searched for a 1" NPS male to 1/2" or 3/4" NPT female reducing bushing, but found nothing. I'm sure someone out there makes an adapter for this application, but I haven't been able to find one. arkie - I just used a standard pipe nipple and it worked fine.

docjenser

Veteran Member

Posts:1400

08 Feb 2014 11:06 PM
Posted By FBBP on 07 Feb 2014 07:14 PM 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? WEL0713 is a variable speed, it pretty much run s all the time at colder temps.What you see that occasionally it shuts off when the hot water safety stops the DSH circulation pump, then the cold water sensor drops because of ambient influence, but you have thermal siphoning with the outgoing water temp getting very hot due to very low flow (coming only from thermal circulation). It is important to understand that the key to hot water making efficiency is not so much the colder water going into the DSH, but to pass on the hottest water to the second tank, so the electric element turns on as little as possible. You want the hottest water on the top, even if you pull in hotter water into the DSH, rendering the DSH a few degrees less efficient. But that slight loss is nothing compared to fresh water coming in too close to the outgoing port towards the second tank.

www.buffalogeothermalheating.com

FBBP

Veteran Member

Posts:1215

09 Feb 2014 12:23 AM
*but to pass on the hottest water to the second tank* That we agree on 100%. Therefore my hang up with stratification. I like the idea of reheating the top water to a point but it may loss efficiency if heated to beyond the set point of the finishing tank. Unfortunately, I believe you give up all that advantage by injecting it at the bottom of the tank. The hottest water joins the coldest water and not much is gained. If we leave the two systems separate, that is, DCW comes to the bottom of the tank via the dip tube and the hottest water goes to the finishing tank through the top, then the tank behaves as designed. Full stratification and hottest to the finishing tank. As soon as we try to splice the DSH into this system something has to give. If we feed the DSH through the element bosses, we maintain stratification. Due to the low input of the DSH, we could do better by reheating the already warm water rather then coldest water, till it reaches the finish tank's set point but in the long run we would not use the bottom portion of the tank. Therefore we need to look at making the DSH more efficient by slowing down the flow. We see from your 0713 that almost no flow gets us 140 give or take so we need to control the flow to maintain the DSH's out put at about the finishing tanks set point.

docjenser

Veteran Member

Posts:1400

09 Feb 2014 02:03 AM
Keep in mind that the bottom is not really cold but gets continuously heated. There is constant circulation through the tank, the tank does not really stratify, since water is continuously circulated through. what you are suggesting will result that water short cycles through the bottom of the tank, which gets hot quickly, and then the DSH safeties kick in around 125F and shuts the pump off. We tested it with the monitoring system, it did not work as well as the above described version. Check out another system, it might give you more clues about DSH performance. Every's heat exchange system is performing less with lesser flow, so slowing dow the flow will not transfer more BTUs. http://welserver.com/WEL0267/ No flow in 0713 will get you 140F, but also flow will get you there. http://welserver.com/WEL0712/is a better 2 stage system, not a variable speed, which behaves different.

www.buffalogeothermalheating.com

arkie6

Veteran Member

Posts:1453

09 Feb 2014 01:56 PM
Posted By FBBP on 08 Feb 2014 07:39 PM arkie - I just used a standard pipe nipple and it worked fine. I figured that with sufficient teflon tape or similar sealant, that a tapered thread pipe nipple or reducing bushing would seal up tight in the straight threaded heater element bung. Did you use steel/iron pipe nipple or something softer such as brass? I was thinking about using a softer brass 1" male x 1/2" female hex reducing bushing and then transitioning to copper for the DSH supply and discharge piping.