Replies

1. 
   davidmeiland | Apr 23, 2009 11:17pm | #1

   I am not a solar expert but here's what I understand. You might benefit from a drainback system using two tanks. One tank (small) circulates water thru the panel when the system runs. When the system is not running the water drains back to the small tank. A heat exchanger inside the small tank is connected to a larger storage tank. Since you previously had freeze damage I would consider something like this. We have installed one solar thermal system, pretty much as described above--small drainback tank, 80 gallon solar storage tank, 50 gallon electric water heater. Water coming into the house is heated in the 80 gallon tank before being drawn to the 50 gallon tank. The idea is to keep the 50 gallon tank from running. Owner has learned things like doing laundry in the afternoon, etc.

1. 
   MikeSmith | Apr 23, 2009 11:41pm | #2

   we've  always  use a  two  tank  drain-back  system

   you  usually  have  a  higher   delta-T  if  you  use  a solar  storage  tank

   than  if  you  use  your  DHW  tank

   your  DHW tank  wants  to  be   say  105  deg  to  say  140 deg

   but   your  solar  tank  can  be  whatever  it   is..  so  say  it  starts  at 80   and  during the  day you  get it  up  to  160

   if  you  had  been  using  your  DHW  tank,  your  system  probably  wouldn't  have  done  any  collection  for  half  the day

   most  soalr  controls  use  a "turn  on pump " at   delta - t  of  say  10  deg and  off  at 5 degMike Hussein Smith Rhode Island : Design / Build / Repair / Restore

2. 
   Clewless1 | Apr 26, 2009 05:34pm | #3

   I tend to agree w/ Mike Smith. Two tanks gives you flexibility and extra capacity for storing excess energy. That COULD be done w/ one, but there may be some logistical issues I can't think of right off the top of my head. An extra tank can be cheap ... I got a used water heater for $0. The heater doesn't need to work. Lots of these available ... just talk to your local plumbing supplier ... he should have one in his bone yard.

   The second tank (place before your conventional tank) acts as a preheater ... so if your storage is only 90 deg ... the conventional heater works a lot less than the say 55 degF water coming in. The energy aspect isn't much different. Hot water is hot water ... takes 'x' amount of energy to heat it up for use. Two tanks have more standby losses ... but properly insulated, this is a small issue.

   If you have freezing issues ... you should have 1) a glycol based system w/ heat exchanger 2) a drain back system that drains into a small holding tank or 3) a drain down system that drains to the sewer (it's a small amount of water). Your system needs to respond to a freezing condition reliably. But that shouldn't be too hard. Controls are the key, though, but this is simple controls, relatively speaking (although older systems seemed to be plagued by control issues for some odd reason).

3. 
   Clewless1 | Apr 26, 2009 05:35pm | #4

   Why do you have to replace both tanks? Are you without hot water right now? Does the preheat (i.e. solar) tank actually leak?