Re: Thermal Collectors / Mirror Concentrators

Dan Lepinski, P.E.

Thermal mass heating systems built into the slab are very low pressure -- not city water pressure. The plumbing is also flexible to accommodate twists and turns. Subsequently, chances of a leak are essentially zero.

Moreover, when a slab is used as thermal mass, it's insulated from the earth during construction by installing a layer of insulating material before the slab is poured. This prevents warmth from the slab from migrating into the soil. It also cushions the slab from earth movement.

Home builders don't install such efficiency measures because: 1) They don't know how to do it. 2) Training in the work costs $. 3) It adds to the overall cost of the home (not significantly .. but "some" cost just the same, which typical builders are loathe to do).

Mike Renner (NTREG member) has thermal heating built into the slab of his home. It's been trouble-free from the day it was built. Hopefully Mike will chime in and give your more information.


On 5/31/21 3:50 PM, Mellen West wrote:
I would never run hot water floor heat piping in a concrete foundation in North Texas.    The soil has high clay content and is “expansive”.   On e little leak can cause a lot of grief and expense.

 I speak from my experience as warranty coordinator for Coleman Homes.  Coleman used post tension to hold the slabs together and slab leaks were fairly rare events but when they happen it was an expensive misery for all.  Just because the Romans did it does not make it a good idea.  Makes great sense for a greenhouse, but not a whole house.  My opinion.



*From:* <> *On Behalf Of *Philip Timmons via
*Sent:* Monday, 31 May, 2021 1:29 PM
*Subject:* Re: [NTREG] Thermal Collectors / Mirror Concentrators


Thanks, Dan.


Understood and agreed.  I think Solar Thermal heating actively heating a concrete slab (usually concrete embedded PEX or other tubing circulating the hot water) would be a GREAT practice here in North Texas -- but I see very little.  Folks with that stay warm even when the power goes out for days.  


Did you look at Saul GriffITH's (et al) "Rewiring America?"   (Very sharp former DARPA guy -- The Sankey Flow Chart at his level detail is worth the read, alone).  They pretty much by-passed any Solar Thermal aspects.  Or maybe I am reading too much towards this -- but it seems like (to me) we are missing a big part of the big picture with US all just going Electricity!    Here is a link if you or anyone is not familiar.  Free Download, donation / membership optional. >>>  



On Monday, May 31, 2021, 12:53:13 PM CDT, Dan Lepinski, P.E. < <>> wrote:



We have a solar hot water system on our house.  I installed it before putting in the solar electric equipment.  Both systems are 16 years old.

Solar hot water isn't "sexy" like photovoltaics.  For instance, we can't give "excess" hot water to our neighbors as happens with excess solar electricity flowing backwards through the utility meter.  When the water gets hot (per the thermostat max setting I programmed in), the system turns off to prevent overheating the water in the storage tank.

Conversely, solar hot water is much more efficient at converting solar energy into heat and hot water than systems that convert sunlight into electricity.  Reports from the Dept of Energy indicate up to 85% of the available solar energy is converted into heating the water.  Newer systems may be even better.  We have two 4'x10' "collectors" that are sufficient to heat water for five people, and still have some hot water left.

Yes, solar hot water systems are still being designed and installed.  Not so much here in north Texas that I've observed, but more so in other parts of the country.

Where electricity costs are high, and natural gas is prohibited (there are places in the US where natural gas is no longer allowed for use in new subdivisions), solar hot water is often combined with solar electricity.  California is at the top of that list.

Current "state of the art" in solar hot water hasn't changed as rapidly as solar electric equipment.  We have two primary topologies: 1) "Flat plate collectors" that to an extent look like solar panels, and; 2) "Evacuated tube" collectors that resemble large test tubes.  Evacuated tube collectors are more expensive than flat-plate systems, but are also more efficient, particularly in cloudy areas and cold locations.  Because of this latter trait, evacuated tube systems are more common in Europe than flat-plate systems.  Flat-plate systems are the majority in America.


On 5/31/21 12:07 PM, Philip Timmons via wrote:
Anyone in the group still do anything in the Solar Thermal Collector / Mirror Concentrators domain?  

Or has that kind of went the way of tail fins and large cars? 

Talking small-ish scale, single house, small business, small process sized operation.  NOT talking about acres of mirrors.  

Seems most things are going the way of Renewable Electricity ONLY, and then using Electricity to heat water, heat (and Cool) building space, as well as heat for small process.   Looked like that is where things were heading in Saul Griffin's  "Rewiring America," and also in practice?   I am not saying that is fact, just what I am observing.  

Is anyone here still using or designing Solar Thermal?  Was looking at reviewing some of what is the current state of the art. 


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