[RE-wrenches] SHW - parallel tanks

[Nathan Stumpff]

Kirk,

We install this standard on basically all of our two tank systems. Small circulator w/ check valve from domestic tank HOT to solar preheat tank COLD. The 'makeup' water for that line is the one already installed, preheat HOT to domestic COLD. It operates on a delta-T control on both tanks, so if the preheat tank is warmer than the domestic tank, it moves that hot water from preheat to domestic. Benefits are increased solar storage (domestic tank becomes usable storage,) cooler preheat tank temps (so better collector efficiencies,) and no backup running when there is low DHW usage and the domestic tank cools off before the preheat tank.

The controls we use (RESOL) have this function preprogrammed, but any controller with a spare delta-T relay could be used if you have sensors on both tanks.

Works like a champ on really simple systems, we have had to monkey around and do some multi-tiered controls on systems with several heat sources to keep it from running at inappropriate times.

I'd be happy to share some drawings off-list if you like.

Cheers,
-Nathan

--
Nathan J. Stumpff
NABCEP Certified PV Installation Professional #091209-175
NABCEP Certified Solar Heating Installer #032412-14
Project Manager | Arctic Sun, LLC
nathan at arcticsun-llc.com <mailto:nathan at arcticsun-llc.com>  | (907) 457-1297
www.reina-llc.com<http://www.reina-llc.com/> | www.arcticsun-llc.com<http://www.arcticsun-llc.com/>
[cid:image001.png at 01CEB93C.3DDDDE90]<http://www.facebook.com/ArcticSunLLC>

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kirk Herander
Sent: Tuesday, September 24, 2013 2:19 PM
To: RE-wrenches
Subject: [RE-wrenches] SHW - parallel tanks

Hi,

Every summer I get a few calls from annoyed hot water customers who can't stand hearing their boiler fire merely to keep the indirect tank up to setpoint temperature, when of course the solar preheat tank is at 160 degrees or better at mid-day. So what's the best way to transfer heat, in essence temporarily putting the tanks in parallel, from the solar tank to indirect? I can think of a few possibilities using a circulator and temperature controller, and a additional connection between the tanks, such as the tank drains plumbed together as a return line, but where is the best place to locate the circulator in a standard preheat arrangement (i.e. hot output of solar preheat plumbed to cold input of indirect tank)?

Kirk Herander
VT Solar, LLC
dba Vermont Solar Engineering
NABCEPTM Certified Inaugural Certificant
NYSERDA-eligible Installer
VT RE Incentive Program Partner
802.863.1202

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