Pond Loop Sizing Question
Last Post 30 Sep 2009 09:51 PM by engineer. 6 Replies.
Printer Friendly
Sort:
PrevPrev NextNext
You are not authorized to post a reply.
Author Messages
geonomicsUser is Offline
New Member
New Member
Send Private Message
Posts:5

--
22 Sep 2009 04:00 AM
Could anyone take a stab at estimating how much pipe I could get away with putting into a cistern filled with 147 cubic feet of water? It is roughly 3' x 3' x 15' and I only plan to use this heat sink for a small portion of the heat load, which is for a small 400 sq place.

Any rough approximate or direction/methods to go about solving would be much appreciated..
jonrUser is Offline
Senior Member
Senior Member
Send Private Message
Posts:5341

--
22 Sep 2009 08:15 AM
How many btu/hr do you want to extract from it?

engineerUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2749

--
22 Sep 2009 08:51 PM
Not much.

I don't mean to be flip, but that's around 1000 gallons of water - not enough to be geothermally useful

It would mostly depend on the material of the cistern wall and the characteristic of the soil touching the cistern wall.

Probably way more trouble than it is worth.

Look instead at an air source minisplit heat pump, Mitsubishi or Daikin, among others.
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
jonrUser is Offline
Senior Member
Senior Member
Send Private Message
Posts:5341

--
22 Sep 2009 10:00 PM

Could be useful if you wanted to store a nights worth of heat for a 400 sq ft place.
engineerUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2749

--
23 Sep 2009 09:31 PM
In that case do a drainback or otherwise freeze protected solar thermal system, not geo.
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
Alex_in_FLUser is Offline
New Member
New Member
Send Private Message
Posts:96

--
30 Sep 2009 09:12 PM
For cooling:

Your question is actually rather complex and highly dependent upon the weather. You are talking about 9261 pounds of water. To get 1 ton of cooling will raise the water temperature about 1.6 degrees. A 400 SF place here in FL would take about a 1 ton unit. On a hot day you would heat the cistern about 12-15 degrees. But the cistern will lose heat via conduction to the ground and evaporation thus day one the temp would not get that high. You will get evaporation at night but no way to say how much heat loss you have as it is largely a function of temperature, humidity and wind speed. As the cistern heats up it evaporates more water thus providing greater cooling (equilibrium).

That said here is a wild stab:
- Typically solar pool heater panels are about 900 BTU per day per SF. A 10 F temp rise takes about 0.9 SF panel per SF of pool.
- So if 45 * 0.9 = 40 SF x 900 = 36,000 BTU per day with 10 degree temp rise in the cistern.

So the cistern could probably provide about 2.5 hours of cooling per day for a 1 ton unit.

The amount of heat available would be far less as evaporation accounts for about 70% of the heat loss of a heated pool.  Thus you might extract 1 ton per day of heat without cooling it drastically.

That is probably as good an estimate as you'll get absent a lot more data. Hope this helps.


Alex
engineerUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2749

--
30 Sep 2009 09:51 PM
Um...I responded thinking a cistern is underground - no surface water exposed to air.

If it is an itty-bitty outdoor pond or pool it might be able to be made to work with addition of a fountain. Then it would function similarly to a wet cooling tower, though not as well. Performance would then depend on ambient wetbulb, wind, approach temperature, etc.
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
You are not authorized to post a reply.

Active Forums 4.1
Membership Membership: Latest New User Latest: janvin New Today New Today: 0 New Yesterday New Yesterday: 0 User Count Overall: 34705
People Online People Online: Visitors Visitors: 163 Members Members: 2 Total Total: 165
Copyright 2011 by BuildCentral, Inc.   Terms Of Use  Privacy Statement