Solar & Hydronic questions

jp_2

have you figured heatloss out of the tank? 90F delta T, surface area of tank at R10?

I get more like 11,000lbs. 10,995lbs.

LouisG

Solar water storage & hydronics

Thinking about adding SHW panels to my roof - 4 panels each of 2.2 sq. meters area = 8.8 m2 total. I want to use this for DHW and as a supplement for my hydronic heating system

I'm considering burying an insulated (R-10)concrete holding tank of 5000 liters capacity below the frost line so I can use that as a summer heat sink for the solar panels and reusing the heat from that water in the winter as part of my heating system.

Insolation averages 3.44 kWh/m2/day in my area. According to http://www.apricus.com/html/solar_energy_calculator.htm the four panels will provide an average of 73,000 Btu/day over the year (about 40% higher in the summer months, but only about 60% of that in the winter).

Maybe I have not had enough coffee today but my math seems to be way off. 5,000 litres weighs roughly 10,000 lbs, and it takes 1 Btu to raise 1 lb. of water 1F degree. If deltaT is 90F (140-50) then I need 900,000 Btu to raise 5,000 liters to 140F, or about 12-14 days worth of summer solar heating (neglecting any losses). Somehow these numbers don't seem right to me. Any thoughts?

Another concern of mine is that if super hot water (180F or higher) is left in a concrete tank for lengthy periods of time do minerals harmful to a hydronic heating system leach out of the concrete (calcium, etc...)?

Does anyone here have any thoughts/experience with doing something like this?

LouisG

I specifically neglected heatloss and only estimated the mass of water - this was a calc done in my head. If I'm in the ballpark (even 50% low after heat losses) who cares - the sun energy is free and summer lasts for more than 2 weeks.

Just really want to get a sense if I'm in the ballpark or nuts for even considering this from a chemistry, and heat gain perspective. I'm pretty happy just using the solar for DHW given the rebates I can get and the displacement of NG for heating the water. The big thing is effectively using the summer solar heat - there's only so many showers I'm willing to take each day ;-)

Typical residential solar philosophy is to use a swimming pool to shed excess summer heat into. I'm just looking at using the heat in a contained subterranean storage tank for later use.

5,000 litres @ 1 kg (2.205 lbs/L) = 11,025 lbs. assuming distilled water and 20 degrees C, but who's counting.

Tank will be insulated to at least R-10, probably R-20 with Dow SM and all joints will be lapped, foamed, taped.

jp_2

heat is free

but the mechanics to move it around cost money.

why take more than you can use? are you really getting ahead with a 3000gallon tank?

you may loose more winter heat than you can gain? thus making it useless in winter?

Unknown

use sand

and save yourself alot of money.Then use geothermal to extract the heat from the sand in winter.
TONY

Unknown

And if you want to skip

the geothermal here is a link with the latest technology..http://www.dlsc.ca/how.htm.
TONY

jp_2

summer or winter use?

what are your plans?

if you have a week or two or three of cloudy winter weather, will you ever be able to charge the tank back up?

reason for calculating the heatloss.

Mark Custis

I am Listening

I am in Cleveland, OH US and am VERY interested in doing what you are talking about.

I too am disapointed in daily BTU out put, but think that the daily solar output can be worked into a real anual average gain.

LouisG

An engineering firm in Holland patented a method (about 12-15 years ago)of using hydronics under asphalt roads to capture solar heat into geothermal and water storage. If I owned a shopping mall or factory with large parking areas...:-)

http://www.roadenergysystems.nl/

LouisG

The intent was to build up a large thermal reservoir during the summer with as high a mass as is reasonably doable in a city home lot, at as high a temperature as possible and use that heat for as long as possible into the fall/winter.

When the solar heat gain is insufficient to re-heat the large reservoir effectively, the solar heat would be re-directed to DHW production alone, or maybe a smaller tank (500 litre)to assist in space heating.

I guess I have to speak with the concrete suppliers about the long-term effects of hot water on concrete, but I was hoping that some people here had some experiences that they could share.

LouisG

The .pdf report about this Alberta project ( http://www.dlsc.ca/reports.htm) is fascinating reading. All this at +51 degrees latitude in an area with often horrible winters.

Let neighborhood associations get the rights to install something like this in area parks in urban environments for retrofit applications. Require all new developments to have something like this - commercial and residential. Couple this with co-generation for auxiliary heating and electrical generation seems to make sense to me.

This is part of what governments need to approve/fund/pilot to tell the Saudi's where they can go.

Unknown

Louis

Roth makes large poly tanks, I believe they market them under the name freilow. They use them for septic tanks and fresh water storage.They are rated for 160 degrees and come in sizes 500 to 1500 and are priced really good. You can then spray foam the entire tank in the pit. If you cant google the tanks or foam tell me and I will look for the brochures, I have them somewhere.
TONY

hot_rod

Know the load first

then decide how much of that you would like to cover with solar. DHW is easy to get to. heating loads take a bunch of panels and storage depending on the solar fraction you are aiming for.

Get a solar design software to run some what if calculations.

RET Screen is a free downloadable one. I like F-Chart. T-Sol does a nice job. PolySun, and a handful of others.

Here is a screen shot of the free demo calculator at the T-sol www.valentin.de

hr

kevin_in_denver_3

long term thermal storage

Your calculations are in the right ballpark, and are trying to tell you that it's not practical.

A local professor tried this with a 12,000 gallon tank. I haven't seen a report yet, but have heard that the standby losses are a lot more than projected.

180F water wants to evaporate real bad, and you can't seal the tank without pressurizing it. Vapor loss is one of the worst things about a big, hot solar tank.

kpc_41

it was my...

impression that SAND was a VERY poor conductor of heat. ex. beach sand.. the 1st 1" layer of sand is hoe but below that it is cool. ..kpc