Solar Hot Water Systems - PV vs delta T control [RE-wrenches]

[Doug Pratt]

From: David Blittersdorf [mailto:davidb at nrgsystems.com]

<snip> I am looking at the trade-offs of going to the PV powered pump
system vs the delta T control. <snip>

Any experience out there?

Hi David,

  In a plain-water PV powered solar hot water system, you WILL get some
cool or even cold water pumped into the storage tank early in the
morning.

  However, the Heliodyne PV powered system uses a side-arm heat
exchanger, and depends on thermosyphon action to pull cold domestic
water off the bottom of the tank, and put hot water into the top. If
there's no heat from the glycol loop to put into the domestic
water...there's no thermosyphon, and you don't lose anything. As soon as
the glycol gets warmed up, then the thermosyphon gets going. Elegant
simplicity.

  If your Heliodyne system currently has the big U-shaped heat
exchanger, you'd need to trade it for the side-arm style when switching
to the PV system. Personally, I'm a big fan of PV control. It's stone
simple, there's no sensors, wiring, or controls to fail, and it doesn't
require any outside power source, AC or DC.

Cheers,
Doug Pratt
Real Goods Technical Editor

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