[Greenbuilding] Simple Solar Radiant System

Tue Dec 5 16:03:43 CST 2006

i used drainback in part because the lift  height from tank to top of 
collector was just 6 feet and the volume of piping and fluid was large and i 
didn't want to buy all that glycol and given the low temps i wanted the 
better heat capacity and viscosity of water. .   in your case the35 foot 
lift and the fact that you can minimize the piping volume and that the heat 
exchanger will either be radiators or the radiant floor mean the glycol 
would be simplest.  (the lift head would be reduced to zero and the pumping 
head would be small so a really low hp pump wuld work. you might consider 
the el sid 10 watt pv powered pump or remember that whatever solar water 
heater pump you are using will work. )
 one way around the lift height in your case is put the drainback tank as 
high up in the envelope as possible. (i saw one such dback tank mounted on 
the floor of the attic with insulation over it.)  the htx  in the actual 
solar storagetank ( or in your case th radiant floor or radiator)  was still 
down in the basement now pressurized by the standing water in the supply and 
return. put the pump low to avoid net negative suction pressure problems at 
the pump inlet.

either system will work, but each has different cost, design and maintenance 
and efficiency issues, most installers like drainback if carefully 
engineered, installed and maintained. it is alwas advantageous efficiency 
wise to eliminate a htex if you can.
----- Original Message ----- 
From: <dantonioli at earthlink.net>
To: "'Drew A. Gillett P.E.'" <deaneg at hotmail.com>
Sent: Tuesday, December 05, 2006 12:07 PM
Subject: RE: [Greenbuilding] Simple Solar Radiant System

> Excellend feedback, Drew!
>
> I'm often inclined toward simple systems and have recently been frustrated
> by radiant folks who want me to sell me a Munchkin boiler, add mass where 
> it
> doesn't exist, and spend money I don't have.
>
> What kind of pump would you recommend? The distance from the office to the
> roof is about thirty five feet. I'll start by pumping liquid through a 
> large
> radiator but might eventually add a few 55 gallon drums in the shop for 
> mass
> (I've got the space for them, they're cheap, so why not!).
>
> Also, I've been wondering if I should use a drainback system or no 
> drainback
> and use glycol; the latter seems simpler.
>
> Dan
>
>
>
>
> well dan, i installed a 7  panel 60 degree slope 4x6  used flat black 
> single
> cover parallel flow solar water collector system a few years back to heat
> the basement floor of my farmhouse.  it is a drainback system (used 30
> gallon horizontal tank) , with used groundfos  pump feeding 4 1/2 inch by
> 200 ft. polybutylene  loops in parallel in 1000 sq.ft. of  4"concrete
> basement floor.
>
> a used controller turns on the pump whenever the collector is warmer than
> the radiant floor return (typicaly 60 on startup and 70 running full 
> out. )
>  the system is left on summer and winter. it ran 2000 sunny hours last 
> year
> .  the basement of a new england farmhouse never overheats even in
> summer.   in winter, the system keeps the basement  comfortable 45-65 and
> from freezing with no other backup heat.
>
> i strongly endorse your concept, use used equipment, minimize controls and
> additional storage. and make sure the collectors are tilted steeply enough
> to shed snow in winter and to reduce gain in summer. good luck
>
>
> ----- Original Message -----
> From: <dantonioli at earthlink.net>
> To: "'Greenbuilder list'" <greenbuilding at listserv.repp.org>
> Sent: Monday, December 04, 2006 11:17 AM
> Subject: [Greenbuilding] Simple Solar Radiant System
>
>
>>I have a solar hot air system on my home that works only when there's
>>enough
>> radiation to heat the inside of the panel to 74 degrees. The temperature
>> hits 74 degrees and a small, 24 watt fan turns on to brings fresh, warm
>> air
>> into the house.
>>
>> I want to design a simple solar radiant system that works on the same
>> principle I have two thermal panels on my roof that will eventually be
>> hooked up to a larger "master plan" system when time and money permit for
>> doing everything right.
>>
>> In the meantime, I want to use them to heat a radiator in my cold, ground
>> floor office that's chilly even when it's warm outside.
>>
>> The model is simple: one loop, filled with water/glycol, and pumped when
>> the
>> temperature hits a set point. When the sun shines and it's cold inside,
>> I'll
>> at least be able to partially heat the space with solar.
>>
>> Yes, I understand that a comprehensive system with storage and boilers
>> makes
>> sense, but that's for later.
>>
>> Does anyone have any experience with such a simplified system and/or know
>> of
>> any Homepower-type articles online?
>>
>> Dan Antonioli
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>
> 