Virginia "Best" Contracor Quote

The Waterfurnace version of the 2 pump variable speed flow center is controlled as described by Doc. The constant speed pump is energized first and the variable speed pump is controlled by the HP based on Min and Max % setup with the Aid Tool.

The Geo-Flo version of the 2 pump variable speed flow center requires a Grundfos controller package to operate as described in their catalog.

 

OK, I see. Is there a concern in using the Grundfos controller package with WF Series-7?

 

Two different things:

Geo-flo has a controller which is either flow rate or delta temperature controlled.
Water furnace uses the Geo-flo flow center but uses (last time I checked) PWM (Pulse Width Modulation) control strategy controlling the pump directly from its control board which turns on the constant speed first.
Beats me why they combine the most efficient heat pump with the least efficient control strategy.

 

Posting overlap.
The best solution is to use the single pump flow center. The 2 pump flow center is only a bandaid if your loop field is not designed for low pressure drop. Plus you are paying for the additional pumping. Using the 2 pump flow center makes your super efficient geo system much less efficient. So why not design it so you don't need a dual flow center.

 

Good points. Thanks you!

 

Today I read a TVA design manual that it is recommended to have 4-6 parallel loops for vertical 1-inch pipes. I have two loops. If I am interpreting this right, with four loops (two per well) that marginally meets the recommended number of loops. It will be interesting to find out the pressure drop calculations and why a two-pump arrangement is needed. From the pump curves, the 32-140 produce a maximum of 35 Ft Hd at 15 GPM. Trouble is, all my questions have alienated me from the designer/installer contractor.

 

The Ground loop is an issue that I haven't known how to evaluate. The contract calls for equipment selection ... "using methods describe[d] by ACCA, Manual J and WaterFurnace GeoLink Design Studio." I calculate the loop specific length as: 540 feet x 12,000 BTU/Ton-Hr / 52,100 BTU/H = 124 Ft/Ton. Should I be concerned that the loop is too short?

 

TVA? 4-6 parallel loop? How deep? how much flow for what size heat pump? That does not mean that 3 x 1.25" pipe does not work equally well.
Maybe it is a good thing you are alienated from the designer/installer.

The arguments that 4 pipes can transfer more heat than 2 pipes. Nor can you apply a simple ft/ton equation. Putting in a 4 ton heat pump would extract almost similar amount of heat over the season for your 52,100 but/h peak load, but if you leave the loop length the same you end up with more ft/ton.
heat pump heating capacity is more in the neighborhood of 10,000 but/ton.

At the end of the day your loop might be long enough if the ground behaves favorable.

What is off is the 6% antifreeze, and the need for a 2 pump flow center.

Lets say you are using 21 % methanol, what you should use in heat dominated climate, and lets say you have 20 ft each way of 1.25"header pipe, and 30ft of outdoor header each way, and 4 circuits of 520ft of 1" pipe, your pressure drop including 10 elbows, heat pump piping etc is around for the total system is around 27.5ft at 15 gpm.

So why is a 2 pump flow center, with a constant speed pump coming on first, better? The only thing it is is much less efficient.

 

It seems we are covering three subjects now.

1) The designed low % methanol should be easily corrected.

2) Pressure drop through the GHEX: Seems the pressure drop is small enough to allow one pump. Good news. I hope the designer agrees.

3) I incorrectly calculated the loop specific length. As i understand now, it should have been calculated as: (10,000 BTU/Ton-Hr) x (260' + 280') / (52,100 BTU/Hr) = 104 Ft / ton. Is this OK with a soil thermal conductivity of 1.80 Btu/(h*ft*°F) and 1.2K grout? I have no idea. I also do not know what the WF GeoLink Design Studio is. I assume it calculates the size of the loop to meet manufacturer's standards of HP performance. Let me know if I am wandering out of my lane here, but, is there any possible issue here?

 

GeoLink is a Waterfurnace software program which is a simplified design software, and also provides an energy and operational cost estimate to compare geo to other fuel sources.
Part of the concern is that the designer actually considers 6% methanol in the loop.
The 2 pump flow center is recommended and sold by water furnace for larger 4-5 ton heat pumps, but is detrimental for efficiency. However, manufacturers are not good designers, and sometimes do not care very much how much pumping power one use, as long as it does not affect the rating of the machine.

Your designer is Rehau LLC. Rehau is a manufacturer of plastic, in this case the plastic pipes, and developed the 4 pipe pex system. Of course they use that in the design proposal. But I question wether they know how design efficient system.
The formula you are using does not calculate loop length correctly. The point with the 4 pipe borehole is that it reduces borehole resistance and can transfer more heat per foot, kind of a similar to using better grout. There is nothing wrong with pex pipe in the borehole (although I would not use it), or putting 4 pipes in a borehole, but there is a limitation on how much you can reduce the amount of earth mass connected to the pipe (borehole length). Soon or later the ground will be the limiting factor, the needle ear.
You loop might perform well. Hard to tell through the internet. I am sure the software might suggest that the lengths is fine. I just learned to question the software.

What is unquestionable a red flag is the antifreeze level and the flow center.

 

The contractor informed me that he designs per IGSHPA and AEE for the % antifreeze by calculating the average of the lowest inlet and outlet water temperatures minus 10 Deg. F. He said some manufacturers recommend 10 F below the lowest outlet water temperature. He asked what I prefer. Not knowing the specifics of thermal performance of the antifreeze/water mixture and what WF recommends, I wrote that I have no preferences other than what will assure manufacturer's warranty. I don't think it should be up to me to state I want 21% Methanol.

The contractor also informed me that he would install one variable flow pump and that there was room for a second pump if required. That makes me feel a little better, but not as good as if he had told me one variable pump is all I will ever need.

The WF equipment is due to arrive tomorrow and is scheduled for installation before the end of the year. Cutting it close. Hoping that I am just a nervous customer and everything is going to turn out great. I am particularly thankful to the forum members for their great comments. I feel I have advocates to help bring about a successful project. Being only on the receiving end so far, perhaps there is a holiday party fund I can contribute to. ;-)

 

You should not design your loop field and specify your antifreeze levels...
Methanol freezes much quicker than glycol, so you want to be at minimum leaving temp minus 10F.
So the question for him would be what min temp he design his loop for.

The loop field should be designed for a low pressure drop so 1 variable speed pump would be enough, again, he determines that with the loop field design.

Are you going with the same design as laid out before? 2 boreholes at 260ft with dual pipe rehab in it?
Total of 4 x 1" circuits?

 

I'm guessing TVA refers to Tennessee Valley Authority.

 

Min inlet T = 36.1
Min outlet T = 31.1

Yes, same design as laid out before: Two boreholes. They were designed around 240 ft each. Drilled 260 & 280 ft (that's another story). Four 1" circuits (two per borehole). Eight pipes come into the house and are tied into the supply and return headers.

 

Good guess. I was researching how to reduce pumping power and came across a TVA document on heat pumps. TVA started getting interested in cutting electric demand in the 70's when the demand grew much greater than hydroelectric power available. My folks lived by Boone Lake in an all-electric house and were researching how to use the lake water for a WSHP. We visited other lake-front home owners that were pumping water out of the lake and into a open-top box with a refrigerant coil in it. Water drained by gravity back to the lake. The lake dropped about twenty feet in the winter and created additional pumping requirements. Anyway, the TVA document caught my eye.