HOW DOES SNOW EFFECT SOLAR THERMAL COLLECTORS?
I have been meaning to address a question that has come up a number of times over the years I have been associated with Thermal Solar Systems, (TSS). I first wrote an article that addressed which collector type, (flat plate or vacuum tube), is more susceptible to collecting snow back in the summer of 2009. The article was very pro vacuum tube based on their superior efficiencies compared to flat plate collectors. I mentioned that “wind and snow simply pass through the openings between tubes and they are virtually unaffected by wind and snow”.
After the article was published I got a number of calls from readers who disagreed with my assessment. They insisted that because vacuum tubes remain relatively cool to the touch, (ambient temperature), that the tube will in deed collect snow and thus have a greatly reduced efficiency when covered with snow. They supported their theory with the idea that flat plate collectors will be hot to the touch when the sun is shining and as a result will melt snow as it falls and / or soon thereafter.
Well, the summer of 2009, when my article was written and published, pre-dated the installation of a Sunnovations TSS on my home. I went into a lot of detail in last month’s newsletter about Sunnovations but I just want to refresh your memory by saying one of Sunnovation’s claims to fame is that they pull a vacuum on standard flat plate collectors. Vacuum tubes are not an option with the Sunnovations system so when I chose Sunnovations for my own home I knew, despite my previous article expressing the attributes of vacuum tubes, that I would be using flat plate collectors…and I was, (and remain), fine with that. The many advantages of Sunnovations, again, which I expressed last month, far out weighed any earlier preference with vacuum tubes.
So, back to the original question…does snow accumulate on flat plate collectors?
The answer is YES! ABSOLUTLEY YES! I have photographic proof!
As you know from last month’s newsletter, I live on a mountain in Orange County, NY that is known as Storm King Mountain…and for good reason! We seem to have our own weather system here. We get everything the town gets but in immensely greater quantities! This past weekend was no exception…we got clobbered by the October snow fall and my two 4’ X 8’ collectors were covered with snow for days. This is not the first time this has happened…I actually had to clean the snow off the collectors after a particularly heavy snow last winter with sustained freezing temperatures for weeks after. Last week, because it was still October, the daytime outdoor temperature rose to about 60 degrees during the day so the snow on the collectors melted with no assistance from me in a few days.
I am still a fan of vacuum tubes in traditional “pumped” TSS applications and I still hold to my original statement that snow and wind will simply pass through the spaces in between the tubes. So, to those who chastised me back in 2009 over this issue, I continue to respectfully disagree and now offer what I believe is indisputable proof! Flat plate collectors WILL hold accumulated snow!
SOLAR START UP GUIDE: HOW TO START A SOLAR INSTALLATION COMPANY
Check out this incredible resource my good friend, Chris Williams of the HeatSpring Learning Institute, has assembled for you. You can see it here.
Another great resource from my friends at HeatSpring. Get the guide here.
Check out this article from Solar Thermal Magazine about the positive perception of solar water heating.
IS IT NECESSARY TO FLUSH AND PURGE A GEOTHERMAL GROUND SOURCE HEAT EXCHANGER?
The answer is unequivocally YES!
I have posted a great new video of Shane Kanter of GeoTemp Geothermal Services flushing and purging a slinky Ground Heat EXchanger, (GHEX) at the Montgomery, NY geothermal new construction site developed by Malmark Construction. I discussed the flush and purge process back in the July, 2011 newsletter but now that I have the video posted I want to revisit the subject. The video documents Shane using a traditional “flush cart” to flush the GHEX of any debris and purge it of air.
- Flush debris from the GHEX
- Purge air from the GHEX
- Verify GHEX design, (pressure / flow)
- Check for possible flow blockage
- Charge GHEX with antifreeze
- Pressurize the GHEX
Let’s review some basic requirements as stated by the International Ground Source Heat Pump Association, (IGSHPA), regarding flushing and purging.
A flow velocity of 2 ft / sec in the GHEX piping will completely remove any trapped air in the loops. The small, fractional horsepower circulators used in many “pump stations” provided by geothermal equipment manufacturers and pump manufacturers will not produce enough flow to meet this requirement…unless, each loop is valved to isolate it from others and the manifold is located in the home as opposed to in the ground. Even then, the small circulator, (in this case a Grundfos UP26-99), may not have enough power to reach the velocity to ensure a thorough purge.
One of the nice features of the “pump station” like the one Shane uses in the video is that it comes equipped with isolation valves to segregate the GHEX from the geothermal heat pump. It is preferred to flush and purge the GHEX separate from the equipment so that debris from the GHEX would not enter the heat pump’s heat exchanger and also devotes the power of the pump to the GHEX without the pressure loss of the heat pump’s heat exchanger. In the video, Shane chooses to flush and purge the entire system at one time…his call to make as he is an experienced geothermal installer and feels that the relatively small amount of pipe in the GHEX, (1500’ of ¾” polyethylene tubing), and his diligence when constructing the GHEX to prevent any debris from entering the tubing will work in his favor.
The flush cart has a pump which generally is either a 1 ½ HP, (for up to 6 ton systems), or a 2 HP pump, (for up to 10 tons). Flush carts can be purchased completely assembled from many GSHP equipment manufacturers and their distributors.
The flush and purge process allows for the introduction of the antifreeze into the system, (the video shows this process). The antifreeze chosen for this job is ethanol based. There are essentially three choices of antifreeze for geothermal applications; methanol, ethanol and propylene glycol. There are some ex-geothermal installers who used methanol….it is VERY flammable and toxic but it was used because it has a very low viscosity when cold and thus was easier to pump, (methanol is now rarely used and in many cases not allowed). Ethanol is less flammable and toxic than methanol and has similar pumping characteristics to propylene glycol. So why not use propylene glycol? Its simple….ethanol cost less and you need a fair amount of antifreeze in these systems.
You can see Shane introducing the antifreeze into the flush cart’s tank…the cart’s pump then forces the fluid into the system. Once the required amount of antifreeze has been injected into the GHEX then the flush and purge process can begin. You can see in the video how you need to initially keep the fluid level in the flush cart’s tank low so that when slugs of air from the GHEX find their way into the tank the fluid doesn’t come gushing out of the tank and all over you and the floor! The entire process can take as much as four hours for a vertical bore hole GHEX because of the large amount of tubing and the likelihood of air being trapped in the vertical GHEX. In this case, the slinky is almost at the same level as the flush cart because these homes have a below grade basement so the process is much quicker…about one hour.
When I was at IGSHPA in Stillwater, OK this past August, they had a simulated GHEX with two loops of ¾” polyethylene tubing with clear manifold piping so you can actually see the trapped air when it occurs…and let me tell you…it DOES occur!
This brings me to my last comment for geothermal for this month.
I had the question of “to flush and purge or not” posed to me by a homeowner in Ohio who found me on the internet. He purchased a new home with a geothermal system that was functioning poorly. I guess he read my July, 2011 newsletter where I first mentioned a flow velocity of 2 ft / sec in the GHEX piping will completely remove any trapped air in the loops. He said he mentioned this to the installer and builder and they both claimed the use of the “pump station” made the system “self purging”. It ain’t so and only if the GHEX loop manifold is in the home, (not in the ground), would you have any chance of it’s circulators sufficiently creating enough flow for a proper purge. So, again, pump stations are NOT self purging!
Next month lets talk about the need for a proper heat loss / gain calculation as the starting point of any good geothermal project. My friend in Ohio’s dilemma reminded me that the job can go bad right from the start if a proper ACCA manual J calculation is not done in the design stage…and it can get worse!
SOUTHERN METHODIST UNIVERSITY GEOTHERMAL MAP UPDATED, NATIONAL GEOTHERMAL DATA SYSTEM UNDERWAY
MU’s Geothermal Lab has recently completed research updating the U.S. portion of the 2004 Geothermal Map of North America. You can read about it at Renewable Energy World.com
I am in the process of securing new training partners for 2012 and I am excited to say that it is very likely that I will have manufacturer and distributor partners for geothermal, Small Duct High Velocity, (SDHV), air conditioning as well as mini-split air conditioning and heating training. Please keep an eye on the “Training Events” section of my website as I will be posting subjects, dates and times as they are confirmed.
ARE YOU SMART ENOUGH TO BE A PLUMBER?
Check out this goofy survey that I found on AOL. It is a gross over-simplification of what plumbers must know but I thought my plumber friends out there might get a kick out of it. Check it out here.