Discussion in 'Open Loop' started by eisensms, Jan 16, 2009.
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Geothermal in Alvin
Your installation should be about $12K to complete. Mark. Allied Air Texas
281-355-0430. Home Cell 713-835-4301.
Why not just use open loop systems?
Lot of good information here.
Just remember these critical issues: what is water quality and quantity ??, water temperature, cost of supplying that water flow: If your well pump motor draws 8 amps @ 240 volts, that too is part of your heating cooling electricity cost. Gonna use city water? Is it free?
A close loop system uses a small circulating pump that may draw 3/4 amp at 240 volts. Assuming that the closed loop system is engineered, sized, and done correctly, and is leak proof, do you see where they would use LESS electricity?
While you are correct HVAC tech, do not underestimate the cost disparity between closed vertical and open loop. You can buy a lot of pumping (and pumps for that matter) with savings.
Closed loop can double a system's cost here.
Here the cost for 3 tons either closed or open is the same. After that point the two begin to seperate at a drastic rate of price increase for the closed loop install and the amount of risk for the open.
In my particular case, I thought about converting my almost new open loop system to closed loop. I know an excellent, experienced geo thermal company out of sumpter, that partners with a driller. We could have dropped a 3 hole vertical bore setup (cheaper) and allowed part of the line to remain submerged in my water at 120 ft. This would have worked very well in my specific area. But I couldn't swing the additional $7,000.00 - $9000.00 cost with one girl in college and the second one getting ready to.
Here the equation would have been: how long would it take to get a payoff on the original $13,000.00 installation + an additional 7 - 9 thousand?
My decision is to stay with open loop. if you order the cupra nickel exchangers, works well, inlet temperatures 58 - 71 year round.
Open loop vs closed
While I'm not a big open loop fan, we have installed many of them successfully. It generally makes sense if you have an existing, or need to install a pump anyway. Since temp is maintained at ground temp all the time, rather than increase or decrease temps gradually, as a loop does, you tend to get higher efficiences. Of course, you also pay higher pumping costs, but I'm told overall you save money. Also remember, in open loop you circulate about 1.5 gallon/minute per ton, vs. 3 or so for closed loop.
My "pumping power" is less than 5 watts, or whatever a solenoid valve uses while open - my well has 9+ psig of static head, more than enough for the geo unit.
the contractor I spoke to today promoting an open loop design advised that going with a variable speed well pump / constant pressure system would negate the claims that open loops consume more energy for pumping due to the technological advancements in these components - can anyone tell me if that is true?
He also advised that I should not consider using a galvanized well casing, but that a PVC well would be much better suited to geothermal equipment. My only concern about this claim was that there is a well-driller 1 mile from me who uses galvanized and I would hate for him to not get the drilling work...
"the contractor I spoke to today promoting an open loop design advised that going with a variable speed well pump / constant pressure system would negate the claims that open loops consume more energy for pumping due to the technological advancements in these components - can anyone tell me if that is true?"
There are a lot of variables to pumping costs. The variables are wire to water efficiency (pump) and volume (gpm's) and static height of water in well and pressure losses in piping and pressure requirements for system and cost per KW for electricity. Also consider equipment costs and labor costs for pump replacement.
A vfd's true claim to fame is the soft start. By eliminating the frequent amp spike conected with start up it consumes less kw than a traditional mechanical switch set-up. The reality of a vfd is that it can cover a wide range of gpm requirements with no drawbacks if usage is reduced seasonaly, or high usage is intermittant.
Comment limited only to energy savings
I am sure that variable speed pump helps. There is no one "right" answer to give you.
Payoff WILL NOT be immediate.
I work commercial and variable frequency drives have come a long way. The commercial ones are generally reliable and ALWAYS justify their cost @ 13 - 20 months later. They are remarkably small these days! I have one exceptional Brown Bovery VFD that is in its 17th year; though it is an exception.
I am hearing good things about Emerson and Franklin Electric. My previous fixed speed 3/4 hp well motor was guaranteed one year. When my well repairman replaced my failed pump motor in Jan 2011 he installed a Franklin Electric 1 hp fixed speed and said he had no problems with them and extended my warranty to two years!
I think that products with good engineering are extending into the residential sizes. Prices are dropping. Is it worth spending $1,100.00 just on a VFD for houshold pump? Labor is additional.
What's your income? What's the warranty? How much lightening strikes in your area? If I was going to install a VFD at your house, I would do it "by the book" and include a COMMERCIAL grade power surge protector for the box. Also you can't rain on VFD's and they shouldn't be in 80% relative humidity. Electronics, right? Find out what Franklin Electric would like to see!
Next point, as a hvac tech, supervisor, I know as well as most of the professionals here that it is good for motors, especially compressors to run for long periods and avoid the on, off, on, off.
A lot of on, off, is especially rough on compressors, that is why running the new residential Copelands on 67% capacity for 5 or 6 months is such a good idea. Running doesn't especially shorten motor life. On, off, and short cycling does.
But here is where I may have a different opinion from some others about short cycling submerged pumps. First, submerged residential sized pumps have lighter, short shafts. Those shafts don't weigh too much. Thus they start up with less inertia.
This is a lot different than say a 7 hp commercial pump that has a bronze impeller that weighs 15 lbs or more.
Two, the submerged pump is, I remind everyone, SUBMERGED in 58 - 70 degree water where I live; colder elsewhere. Heat in the windings dissipates to the housing immediately! I hold that if the motor receives 240 volt power and you have 10 gauge copper wiring in top notch condition, that motors in the 1/2 - 1 1/2 hp range do not suffer at all.
Contrast this to one of my 1980 hermetic 250 ton centrifugal chillers. Start up is over 460 amperes of current for 3 seconds at 460 volts.
Trane specifies that this chiller WILL NOT restart more than two times each hour, (and the factory timer will not allow it to do so), to avoid overheating internal windings and having catastrophic electrical winding burnout.
There is also a argument for sizing residential well pump motors pretty exactly (and not oversizing) which allows a traditional pump to run efficiently at rated speeds. Remember that as long as you have ENOUGH pumping capacity, (water still comes out of your faucetts and shower at normal pressure) it doesn't hurt the well pump motor to run a long time.
Additional response to notification in my box
A well engineered and well executed closed loop system will be more energy efficient than an open loop system. The cost of the loop starts at $8,000.00 and then goes higher based on specifics of ground, locale, and tonnage.
Open loop systems use more energy than closed loop systems. Variable Frequency Drive will drop pumping costs a bit: 3 - 8%. That is considered a decent compromise. You want highest efficiency, you pay for closed loop.
Thanks so much for the great response! I was leaning towards the closed loop and I thnik your response just helped solidify that decision. While we know the water has been good here for the past 40 years, who knows what tomorrow may bring. A 5 year drought could change things, so could many other environmental impacts.... I also like the simplicity of the closed loop - seems to be less room for failure and I certainly like the less maintanence aspect. I already work full time and run a small grain farm part time - the less maintanence I have within the home, the better!
Please do not make broad sweeping statements of opinion, There is allways a "right" choice for the system chosen and it is very job, location, and consumer specific.
I'd argue the biggest claim to fame for variable speed pumps is when the job calls for not only varying volumes, but also pressures. My standing column system utilizes a variable speed pump operating in two modes:
1. Domestic House Use; 12 GPM, 200 feet total head @ 7.0 amps
2. Geo operating; 7 GPM, 70 feet total head @ 1.5 amps
If you can take full advantage of the pump curve, nothing can touch variable speed for efficiency!
I am ALWAYS convinced by the "amprobe" meter. Tremendous!
I need to decide about open v. closed loop in NE Pennsylvania. I have an existing well with a dead pump. For household water, I'd need to replace the pump : estimate $1500.
I've got one proposal for a pump and dump:
new well will a Gould BF 20 flow controller and 15 gpm pump (not sure if this is really vfd or not)
5 ton waterfurnace, cupro/nickel
dump to existing well
high static water table - ~ 10' below surface.
Or a closed loop system, again waterfurnace, for $32,000 - but then I need to put in new household water pump - $1,500. So ~$33,500 total.
And there's iron in the water. Not enough to taste, or see in the water, but leaves red in toilet bowls.
Is the extra $4500 worth it?
How easy is it to descale/clean the heat exchanger? Is it just a matter of running fresh water through it once a year??
I'm really surprised by how close those costs are. Your loop field must be a pretty easy dig!
For a single-pump pump-and-dump with house service (even with a high water table) your pumping energy will be high enough to lower your installed COP considerably. The reason is that the pump is pumping all the water up to house pressure first, then a portion is split off to run the geo. I've shown that there is a way around it - a dual pressure, single pump design - but given the blank stares I received when I first proposed it to my well contractor, I'd say it's going to be awhile before this catches on. (He guffawed when I showed him the specifications of the pump I was going to use - half the size of his typical installs)
If you have questionable water, I've heard it can get even worse over time when subjected to to demands of geo pumping. Easily 10x that of domestic use.
Short of a bigger break in price, and a willingness on all parties parts to go with an unconventional pump control protocol, my vote in your case would be closed loop.
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