Utah Looking for some advice

A friend of mine asked my opinion about this design. The loop circulator shown will cost him about $900.

I told him that I knew where I could get some experts ( you guys ) to weigh in this.

Is there a better, more efficient, less expensive way to do this?

 

Wet rotor pumps are a non starter for me anymore. I also ONLY choose variable speed pumps when the usage/demand absoloutly warrant them as a choice. The words more efficient and less expensive also rarely go together in the same sentence. I would install a single speed pump and lose all the add ons, or go non presssureised single speed for that small of a total load.
Eric

 

My first thought is "how do you fill the system"?

 

Yea, they kind of forgot the purge ports. He is planning two valves at the 90's in the lower right of the drawing.

 

What Pump would you suggest Eric?

 

He only needs 9 gpm, I would use a wilo stratos. You would need a pump which makes about 24ft/hd at 9 gpm but throttles back when less flow is needed.
A 1.25x3-25 would do it.

http://productfinder.wilo.com/en/GB/product/000000100002f6920004003a/fc_product_pumpcurve

Personally I don't see a need for balance valves, it will just add flow restrictions, which requires more pumping power. With 3 heat pumps being fed, the runtime of the circulation pump would be very high and it would use a high amount of electricity if it is not a variable speed.
The final design (and the pump) depends on the length of the piping to the individual heat pumps, it diameter, and the type of pipe. Copper not being great for pressure drop, but here it might not matter due to the low flow requirements.
The D/C inverter driven pumps are not cheap, but they give you the needed efficiency at the increased runtime.

http://welserver.com/WEL0877/

link above is same concept, just more gpm, and 2 circulators for redundancy.
Give me the pipe lengths to the heat pumps, and the details for the loop field, and I can run the numbers.

# of loops, lengths of circuits, lengths of header pipe, lengths inside, lengths to the heatpump from the header t's, you know the drill.

 

BGM 136 from flowcenter products. Set it and forget it. A tried and true work horse driven by bell and gusset. If you do need to replace the pump, it is available at almost every supply house nation wide.
Eric

 

I'm with Doc on the "balancing" valves.

 

I would be concerned about the running time given that it serves 3 heat pumps. Chances are that the pump sees many hours at reduced pumping power needs when only one or 2 HPs are running. Using a constant speed pump would significantly effect your system COP or EER negatively. I understand Eric's "reliability" standpoint, I look at it from my "efficiency" point of view. Plus I never lost a variable speed Wilo on the source side.

 

So I have been noodling this for a couple of days and I am drawing a blank. Other than the cost to operate a single speed pump, how does it effect the COP and EER? I circulate the same amount of fluid through all the units regardless of the compressor being on to use it or not.
Eric

 

Each heatpump has motorized zone valves, which shuts down the flow to the heatpump when the HP is not running. Given that a majority of the time the whole system will run in part load, having a constant speed pump serving that part load flow need with the full pumping power is very inefficient. In addition, since many times the zones will likely run at different times, the overall run time where at least one zone will be significantly longer. Keep in mind that half the flow now also requires only 1/4 of the pumping power.
The most efficient way, in my humble opinion, is to shut down the flow to each heatpump, as described in the diagram, and have the pump completely turned off when none of the zones are calling.
Just a real life example: A variable speed uses 16 watts to pump 5.1 gpm through a variable 3 ton system, but uses 85 watts to pump 9.5 gpm, which occurs rarely. Average wattage is 33 watts. The system runs 6100 hours annually. A constant speed pump like the B&G would be around 230 watts. 201 KWH versus 1403 KWH. At 13 cents/kwh, the difference would be $26 versus 182$ annual pumping costs. Quite a difference in system COP and EER for a 3 ton system, where total cost to run the heatpump itself might be $300-400 annually.

 

The home owner is reading this thread. He appreciates hearing all of your thoughts.

 

I missed the zone valves... I never install them. Soooo if you vary the flow using zone valves, you are forced to use a variable speed pump. lose the zone valves and you can lose the variable speed pump.
Eric

 

Sure, but if only one 1/2 ton heatpump is running, why would you pump 9 gpm through the whole loop field and all the heat pumps, meaning that roughly 80% of the flow would bypass the running heatpump. Why would you pay 15 as much for pumping energy when not needed? Why pay a lot for an efficient geo system and then have an inherently inefficient pumping solution? Constant pressure, variable speed pumps are the way to go in multiple HP applications.

 

Before this goes any further I am going to state emphatically that we are going to " Agree to disagree ". There is no right or wrong answer here, just 2 differing opinions and ideas about the application of geo thermal design in a residential application. If the fluid is moving and the exchange is being carried out, we have achieved a geothermal solution that is far and away more efficient than anything else we have to choose from now. How efficient or close to " net zero " you design or operate your system is a choice. I seek to strike a reasonable balance between upfront install costs and effeciency in operating cost vs. the other available options.

I have made this statement many times in the past and I will repeat it again. No offense intended to Curt or our other engineering friends.

I am a technical diver, and when talking about decompression theory this a common mantra in regard to the exactness of the exercise:
Measured with a micrometer
written in chalk
and cut with an axe

It is the definition IMHO between exactness of theory and actual application.

Eric

 

here is the design with pipe lengths for you doc.

 

Well, sometimes theory and actual application is very close together.

Certainly there are always many ways to do this, but pumping efficiency is an important impact on system COP and EER. Lets look at the system Dewayne has posted here, 3 heat pumps, a 1/2 ton, 1 ton and 1.5 ton. In a setting like this usually not all the heat pumps serving different zones, are running at the same time. If you remove all the zone valves and put a constant speed B&G pump there, and the 1/2 ton unit turns on, it will consume 300 watts, with 240 cfm airflow, 1.5 gpm flow and 60F EWT. It has a nice EER of 21.3, according to the CM performance tables.

But in real life you have to add the 230 watts from the constant speed pump to the power consumption, meaning your system EER drops from 21.3 to 12.1. Now I would argue that under those conditions we made our geo system less efficient than a new energy star rated conventional A/C unit. A variable speed pump consuming 15 watts under those conditions would take the EER down to 20.3, a significantly lesser impact.

The impact of the constant speed pump is less the more heat pumps are running, and the higher the capacity of the ones running is. We see about 75 watts pumping power used for 9 gpm of flow for a 3 ton system. Since the 1 ton HP uses 650 watts under the above operating conditions, and the 1.5 ton uses 1050 watts, using a variable speed will save you only 7% on the EER if they all run at the same time. But again, most of the time a system like that will run in part load with a significant longer run time of the circulation pump, with the B&G having between 7 % and 40% impact on the system EER, compared to a variable speed, with the average probably around 25%. Even if you measure it with a micrometer, the electrical consumption of those are real, and might impact the operational costs for the geothermal customer more than the decompression affects your own personal physiology as a diver.

In a system like the one above, which costs maybe between $30-40K, it is certainly a choice as you argue, to pay $900 (before tax credits) more for 20-25% more average efficiency via a variable speed circulator. I always believe that you have to create value, and I pride myself for adding value through efficient designs. Many of my customers are not just trying to save money, but also buy geosystems to maximize the efficiency, but not to the point of no return.

Those I own going the extra mile, which is easy in this case. A variable speed pump and three zones valve would do.

 

Dewayne, just to be clear.
1) The numbers are inches, correct?
2) Copper or HDPE for the inside? SDR11? HDPE has a different pressure drop than copper.
3) What is the CV of the zone valves.
4) Distance from the T to the individual heat pump (1 way)?
5) Length of the header trench outside?
6) 50" from the inside entrance point to the air separator, correct? 20" to the pump. Then 80" to the 1st T. 30" between the Tees.

 

Location, location, location. Geo is done in my OA every day of the week for 6k a ton. Meaning this system would go in for 18k turn key, including my drilling and pump work. Does that change the eer or cop? No. But the systems we install are cheaper to operate than any other method of hvac in my OA.
Again, mileage does vary.
Eric

 

Doc,
1)Yes the numbers are in inches
2) inside pipe is copper
3) not sure what "CV" is
4) 24"
5) correct

Thanks so much for your help