Process Cooling
  Home
  Subscribe
  eNewsletter
  Online
  Calendar of Events
  Blog
  How To Corner
  Current
  Industry News
  Company News
  Did You Know...
  Online Now
  New Products
  The Glitch & The Fix
  Resources
  AEC Store
  Archives
  Career Center
  e-News Archives
  Industry Links
  Market Research
  Radiant Flooring Guide Directory
  Digital Radiant Flooring Guide
  Radiant Heating Report
  Solar Thermal Report
  R+H Info
  About Us
  Contact Us
Search in: EditorialProductsCompanies

So You Want To Go Solar
by John Siegenthaler, P.E.
April 28, 2008

ARTICLE TOOLS
EmailEmailPrintPrintReprintsReprintsshareShare



The Glitch

Overview: Given all the recent interest in solar domestic water heating, Joe Wrenchturner decides to have a go at it. He orders some goodies through the Internet store Solar-Is-Us and installs them according to the schematic below.

Exercise: Can you spot a few “minor” details that should be changed before the sun shines on this installation?



The Fix

1. All closed-loop piping circuits with a heat source must contain a pressure relief valve and an expansion tank. Without them, you’re going to have a mess when the weakest piping component in the circuit lets go with superheated glycol ready to blast out.

2. The collector circuit must include a check valve to prevent nocturnal cooling caused by cool glycol in the collectors descending down the supply pipe as warm glycol from the heat exchanger rises up the return. Trust me, this can dump an entire tank’s worth of heat back to the atmosphere in a few short hours.

Note the check valve has been mounted between a pair of purging valves in the Fix schematic. Add glycol solution to the circuit using the left-side valve and remove purging flow through the right-side valve. The differential pressure associated with purging keeps the swing check backseated and eliminated the need of installing a ball valve.

3. The PONPC (Point Of No Pressure Change) still applies in solar circuits. Mount the circulator to pump away from the expansion tank location.

4. Although the Glitch system may operate, it’s not going to perform well with the collector temperature sensor mounted on the inlet rather than the outlet of the collector. This sensor should be as close as possible to the collector outlet. Mount it tight, and be sure it’s wrapped with insulation.

Also, be sure that no moisture can get into the wiring splice between the collector sensor and the cable back to the controller. Moisture leads to corrosion, corrosion leads to resistance change, and resistance change in a thermistor sensor circuit leads to inaccurate temperature information and poor control.

5. NEVER, NEVER, NEVER install a solar domestic water heating system without an anti-scald rated thermostatic tempering valve between it and the plumbing fixtures.

6. I would recommend a microbubble air separator in the collector circuit, and generously size the expansion tank to accommodate a bit of extra glycol solution to make up for eventual air elimination.  

7. Put a good-quality float-type air vent ― one that’s rated for “solar duty” ― at the top of the system. Set it on top of a ball valve that can be closed after the system is deareated. The latter protects the vent mechanism from potentially high temperatures (think 350+ ºF) when the collectors stagnate. It also allows for easy servicing of the vent if needed.



John Siegenthaler, P.E.
john@hydronicpros.com
John Siegenthaler, P.E., is principal of Appropriate Designs, a consulting engineering firm in Holland Patent, N.Y., and author of the text “Modern Hydronic Heating.” Visit www.hydronicpros.com for information on new software for hydronic system design and documentation. John is also the contributing editor to PM's monthly "The Glitch & The Fix" column, which offers hydronic troubleshooting solutions in conjuction with the magazine's twice-monthly Radiant & Hydronics eNews newsletter. You can reach John by e-mail at john@hydronicpros.com.

Links

|PrintEmail
  Comments (1)Post a Comment
Title: Int'l Res Code


2006 IRC section M2301.2.8 "Valves shall be installed to allow the solar collectors to be isolated from the remainder of the system. Each isolation valve shall be labeled with the open and closed position." Do you install isolation (beyond integrated circulator isolation valves shown)?


 

No HTML or BBCode in comments please.
 











BNP Media