Why not do open loop system?
Last Post 23 Nov 2009 08:25 AM by joe.ami. 25 Replies.
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dkubarekUser is Offline
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19 Nov 2009 05:29 PM
I was set on a closed loop system in Pennsylvania when a GC told me to consider an open loop system instead. The close loop system was going to be pretty standard. 3 ton system, grouted, reverse flow, 3 200-ft wells. Price about 7-9k.

BUT, I called the well/geo driller and he said he could also do an open loop system AND residential well (which I need) for less than that. Probably 6-7K for the whole shebang. 200 foot water well, return well (whatever it's called) pump and pressure tank. He said it's not certain because I need enough water to supply my family and the furnace. House is 2,000 sq. ft., 3 tons, either Tranquility 27 or Waterfurnace Envision.

Should I be concerned about the impact on the water table especially contamination? Should I be concerned about maintenance costs with open loop? I see they are very efficient and the neighbors all get about 8-10 gal. per minute flow in their wells.

Any help is appreciated. Thanks.

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19 Nov 2009 09:59 PM
Before an open loop can be considered the water must be tested and checked against the manufactures recommendations. If it does not pass do not do an open loop, warranty issues could arise.

Minerals in the water will scale the heat exchanger and require back flushing to clear them. How often this needs to be done depends on the water quality and run time of the system.

Water usage is always a concern. A three ton unit requires about 5 GPM to operate. That's 300 gallons every hour of operation. Your contractor should provide the annual cost estimates to run your system. Part of that will show how many hours your system is expected to run...Do the math  to see how much water is used.

Bergy


dkubarekUser is Offline
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19 Nov 2009 10:49 PM
So, am I correct in assuming it is possible that the efficiency gained from an open loop system could be spent on increased operation of the pump?

In getting geothermal, I want a system that is efficient, comfortable and low maintenance. I'd rather pay more money now and not have to worry about increased maintenance costs. The new guy I'm working with is IGSHP certified and although I haven't spoken to him yet his assistant says he'll take all the info and alert me to my best option according to Waterfurnace's guidelines.

Is it just a matter of getting a water quality report (water has some sulfur and is fairly hard) and deciding? Or are open loop systems always more trouble than closed loop? Saving 5K sounds great but not if it leads to headaches.
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19 Nov 2009 10:53 PM
That Sulfur in your local water may be a problem for an open loop since it is often an indication of iron bacteria which tend to scale up the heat exchangers   Open loops certainly have more maintenance issues than closed loops (i.e. yearly flushing of the heat exchanger, replacing pumps etc.) that the average homeowner often doesn't want to deal with.
 
Per above, you also certainly have to evaluate both water quality and quantity and you need your well installed before you can do either.  Those wells that are in the Devonian Marcellus shale as yours likely will be are very hit or miss on quantity, generally soft in hardness, but do have sulfur and iron bacteria problems.

Lastly, you need to figure out where you are going to put all that water.  PADEP has made it clear that they are against open loops as they don't want to see the groundwater withdrawn and not replaced, but they are currently legal.  However, the responsible thing to do if you are concerned with lowering the water table is to put in a second re-injection well downgradient of the supply well.  The reinjected water thus has no impact on the water table since you are putting the water right back.  Otherwise you have to figure out somewhere to dump the water (i.e. nearby stream, pond, etc.).

-Adam
dkubarekUser is Offline
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19 Nov 2009 11:18 PM
Adam,
Yes, the water will be reinjected to 60 feet below. But your other points are good ones. I'm one of those guys who would rather pay 5k extra and not have to flush the system, etc. And I want to be environmentally responsible with the installation.
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19 Nov 2009 11:23 PM
Closed loop will be less problematic. Cost of running a pump may well be higher with an open loop system, depending on the depth the water has to be pulled up from.

If you do decide to go with open loop – go all the way with passive cooling! That way in the A/C mode all you’re running (basically) is the well pump and the blower motor. If you were looking at a 3-ton unit, how does a cooling COP of around 27sound?

SR

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20 Nov 2009 12:01 PM

I built new and put in a variable speed wheel and open loop Climatemaster 27.    This saved significantly on cost as I needed a well anyway.   For discharge....  I included a separate oversized drainfield just for the heatpump discharge water. 

My water was a little over manuf. recommendations so I knew I would have to faithfully clean the heat exchanger.  I did have not traces of iron or sulfer so that helped me make the decision.   I also ensured that everything was done to make an easy/cheap conversion to closed loop if I should decide to do that in the future.  So far it hasn't been a problem and in 20 months since startup, I have determined the system has about payed for the difference between (open loop geo and high efficenct propane furnace - difference was roughly $3500). 

As a plus, with the variable speed pump on my well i have constant pressure on my well.... and TREMENDOUS well capacity (and don't have to worry about pump cycling).  It can supply just under 30 gpm @ 60 psi.  THis works great for my sprinkling system (less zones and quicker watering).  

Anyway, I do see dirty solution come out when cleaning, so I would not recommend exceeding manufacturers hardness recommendations.    And if you can come up with the money the closed loop, low maintenance option I think would be lots nicer.  Plus if you go large enough on your loops/borefield shouldn't you be able to get about the same stable temperatures as open loop?!?  (Payback on the larger loops might be unnacceptable ??)

Anyway, well pump does eat into geo savings.  For perspective my well lifts the water 65 feet and at 4 gpm it takes 84 watts,  at second stage (6 gpm) it takes about 1030 Watts.   I figured this the old fashioned way counting meter rotations over long periods and average to get a solid base number then turning on the pumps and observing differences.  Tedius but cheap!!

I thought about passive cooling (with 52 degree year-around water temps..  but with all the coils I've modeled I don't get enough dehumidification).... up where we live that's all you really need is dehumidification.  Sensible load is minimal in most houses.   Anyone else find a successful way to use passive cooling in mild, humid summer climates??

 

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20 Nov 2009 02:21 PM
Posted By Bergy on 11/19/2009 9:59 PM

Water usage is always a concern. A three ton unit requires about 5 GPM to operate. That's 300 gallons every hour of operation. Your contractor should provide the annual cost estimates to run your system. Part of that will show how many hours your system is expected to run...Do the math  to see how much water is used.


Water usage shouldn't even come into the equation for an open loop system. With a return well, the impact of the water table is minimal.  Also with pretty much constant EWT of around 50 degrees vs a closed loop that is pushing 30 degrees or less by the end of the heating season, open loop system are almost always more efficent to operate. While it's true it does use more energy to draw the water up from the well to the geo system, as compared to a horizonal closed loop where you only need to cycle it thru a pretty much flat plain, the impact is minimal, and it proably even more efficent when you consider pumping water though several vertical closed loop wells. 
 
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20 Nov 2009 02:26 PM
Posted By dkubarek on 11/19/2009 11:18 PM
Adam,
.... I'm one of those guys who would rather pay 5k extra and not have to flush the system, etc. And I want to be environmentally responsible with the installation.

What's not environmentally responsible about open loops?

Down2Earth GeothermalUser is Offline
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20 Nov 2009 02:34 PM
Posted By TechGromit on 11/20/2009 2:26 PM
Posted By dkubarek on 11/19/2009 11:18 PM
Adam,
.... I'm one of those guys who would rather pay 5k extra and not have to flush the system, etc. And I want to be environmentally responsible with the installation.

What's not environmentally responsible about open loops?



I was referring to those open-loop systems that dump into a stream, ditch, or other surface-water body rather than returning the water back to the subsurface via an injection well or leach bed. These systems use a lot of water and can have negative impact on lowering the local or regional water table.
dkubarekUser is Offline
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20 Nov 2009 04:45 PM
Jokin,
When you say you see a dirty solution at cleaning the heat exchanger does that dirt come in contact with the water in your home? I'm not familiar at all with heat pumps or what part you need to flush so I could be way off. The system described to me was an open loop that pumped enough water for the furnace and household usage. I'm guessing that the well water enters a pressurized tank and is then split between the heat pump and my water lines so that water doesn't enter the heat pump and then exits to my water lines. Is that so? Sorry for being so dense about it all. I'm in over my head with all these home buying decisions.
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20 Nov 2009 08:41 PM
Posted By TechGromit on 11/20/2009 2:21 PM
Posted By Bergy on 11/19/2009 9:59 PM

Water usage is always a concern. A three ton unit requires about 5 GPM to operate. That's 300 gallons every hour of operation. Your contractor should provide the annual cost estimates to run your system. Part of that will show how many hours your system is expected to run...Do the math  to see how much water is used.


Water usage shouldn't even come into the equation for an open loop system. With a return well, the impact of the water table is minimal.  Also with pretty much constant EWT of around 50 degrees vs a closed loop that is pushing 30 degrees or less by the end of the heating season, open loop system are almost always more efficent to operate. While it's true it does use more energy to draw the water up from the well to the geo system, as compared to a horizonal closed loop where you only need to cycle it thru a pretty much flat plain, the impact is minimal, and it proably even more efficent when you consider pumping water though several vertical closed loop wells. 
 
TechGromit,

Not all areas of the country allow re-injection so yes, water usage IS a concern.

Bergy

waterpirateUser is Offline
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21 Nov 2009 04:57 AM
Please lets not disseminate information that is false or misleading to people seeking understanding and knowledge. One more time for those not fully understanding the concept of loop design and efficency. The anticipated ewt and lwt are all functions of the design process. Loops can have any lwt or ewt that you select during any time of the year. The efficency of a closed loop is exactly the same as an open loop for any given ewt. A open loop system is a way that you trade off up front cost per ton for cost of pumping and the potential for ongoing maintanance if water quality is marginal to manufacturers spec. I would purchase the one that you feel most comfortable with based on budget/garrauntee's offered and enjoy.
Eric Sackett
weberwelldrilling.com
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Spruce LakeUser is Offline
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21 Nov 2009 10:48 AM
What is WaterFurnace hardness recomendation? Can a homeowner clean the heat exchanger?

Thanx in advance!
engineerUser is Offline
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21 Nov 2009 12:49 PM
350 ppm

Download and review page 7 of IM1585 from here:

http://www.waterfurnace.com/literature/

I don't see why a homeowner couldn't clean heat exchanger. Have installer make provision for isolation valves and flush ports. Cleaner will be acidic, so be safe.
Curt Kinder

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill

www.greenersolutionsair.com
fsq4cwUser is Offline
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21 Nov 2009 04:36 PM
I would caution that this procedure might be done at one’s own risk, as any damage to the system would likely void the warranty. Cheap insurance would be to have this service provided by the installer. This is not a bag I would want to be left holding! SR
dkubarekUser is Offline
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21 Nov 2009 04:55 PM
I think my water will be much softer than that. I homebrew so I'm pretty knowledgeable when it comes to water hardness and mineral content. It's probably around 100-150 ppm. But Waterfurnace mentions that a little bit if sulfur is too much and as Adam mentioned Iron could be an issue. My driller mentioned that it's not a done deal. He would need to test the water quality and quantity before continuing with open source. He advised doing the well early on (which I need a well anyway) and going from there.

Does the heat exchanger need to be cleaned annually or more? Also, is it costly? Now I'm thinking it wouldn;t be bad forcing myself to get annual maintenance from the installer. Waterfurnace says the unit I want has a heating COP of 4.2 for closed loop and 5.0 for open source groundwater. That seems like it's quite a bit more efficient. But is efficiency reduced in between coil cleanings to the point of where it's less efficient than closed loop between maintenance calls?
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21 Nov 2009 08:30 PM
Posted By waterpirate on 11/21/2009 4:57 AM
The efficency of a closed loop is exactly the same as an open loop for any given ewt.

At the same ewt temperature, yes.  But a close loop ewt is higher at the beginning of the heating season, then a open loop well ewt, thus more efficent.  This is caused by the summer months of heating up the ground.  As the heating season wears on and heat is extracted from the ground the ewt from the ground loop drops off, but the ewt from the well remains constant.  A wells heat sink is a thousand times bigger than any closed loop system.  Once the ewt from the close loop drops below the ewt from the well, the well is more efficient.  I don't have exact figures of when this occurs, it would all depend on how much heat your drawing out of the ground to heat your house. I would guess that the balance point is somewhere within the first 1/3 of the heating season.

 
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21 Nov 2009 08:48 PM
Those COPs are for a given set of airflow, water flow, and entering water temperatures. Open loop tends to make the unit more efficient since the water temp is typically closer to the ground temp. That gain may well be more than lost in the form of increased well pump power. Delivering open loop water typically requires much more pumping power than circulating closed loop water.

It should be relatively easy to detect scaling, especially in cooling mode. All it takes is measuring the compressor amps when the unit is first placed in service and measure it occasionally. Scaling will push up compressor amps and reduce efficiency and capacity. This can be quickly measured with a clamp ampmeter, but it requires knowledge of and close proximity to exposed high voltage wiring. The amp check is not valid for heating mode - if anything, in heating mode amps will fall as the coax scales up, though capacity and efficiency will both be reduced in either mode.
Curt Kinder

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill

www.greenersolutionsair.com
waterpirateUser is Offline
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22 Nov 2009 04:58 AM
The point being if you design a gshx for a ewt of 55 the two machines exibit exactly the same amount of efficency. If you design for a ewt lower than that to get the "pendulum sffect" from the gshx than the data would bear out that 1/3 of the year you are super efficent cooling, and 1/3 of the year you are super efficent heating, and the other 1/3 you are even. If you average all of that data I am betting that you are pretty damn close to being dead even with the 55 constant ewt of the open system.
Eric Sackett
weberwelldrilling.com
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