Iowa WF Series 7 - FCV2-GL

I have read a some post regarding this flow center and wanted to clear some things up.
Does the series 7 always run the constant speed pump? The system defaults for the Variable speed are 50% to 100%. I would think that you would want the Variable speed pump to be the only pump on from 0-50% and the constant speed pump should allow the variable speed to modulate from between to get a total of 100%.

A 5 ton series 7 requires a min flow rate of 5 GPM for a closed loop and 18 for a max.
On heat 2, the VS pump output is 16 % with a flow rate of 13.1 Gpm.

Shouldn't the constant speed shut down and the variable speed should be able to cover down to the limit that should be 5 GPM?
Any time the unit is on I show Loop Pump K5 on.

 

For some reasons they have the constant speed pump come on first when compressor is at stage 1-6, only above stage 6 the variable speed pump kicks in. They have the most efficient heatpump on the planet, only to combine it with an inefficient pumping solution.
We only use FCV1 flow centers for single heatpump installations. We use different flow centers for multi heatpump applications.

The 5 ton does not require that amount of flow, but operates "optimal" under those flow conditions.

 

Is there anyway to reverse this So the variable speed comes on first then the constant speed on stage 6?

 

Not to my knowledge. Waterfurnace was uncomfortable of pumping through a non energized constant speed pump.

 

That makes sense, but you would think that they would suggest just using a variable speed then since it could handle the flow rates in *most* situations.

 

Again, it beats me. They could have used a larger variable speed pump, use Wilo instead of Grundfos for example. They are really good in building heat pumps, but it is the whole system which has to be designed efficiently.

 

Thanks for the input.
Isn't the wattage estimated on the flow center in the AWL anyways?

 

Yep, that is fine since the pumps use a know wattage at a certain setting.

 

Well, if yhe flow center ever craps out, I will request a variable speed only!

 

talked to WF trainer about this. He thinks tech support has a way to field wire/reverse the process so that the variable speed pump comes on first..

 

I would think this would be a programming fix more so than a wiring fix. Curious what they would suggest.

 

Again, there was a concern from Grundfos that they don't like water to be pumped through their variable speed pump when it is not energized. Not sure how valid that concern is. They should have just taken a larger pump. Or one should design for ultra low pressure drop so one variable speed pump is enough. But don't forget the Reynolds number ...

 

Show me the concern.

 

Ask Grundfos, not me. That's what they told people. Not sure how valid that is.

 

I want to touch on this topic again, because I am still interested if this is possible.
I was watching a video on the UPC-GEO flow center controller and this controller operates the VS pump before operating the constant speed pump by design. How would this be any different than if the Series 7 operated the Variable speed pump first?

Also couldn't one use this blank off plate to remove the constant speed pump and solely operate on the VS pump if it could accommodate flow requirements?

 

Both things are possible. Geo-Flow in my opinion does a better job in controlling the pump strategy. Best way of course is to design the loop field so you need only the VS pump.
What is your flow now when both pumps are running?

 

As you know, flow when both pumps on is a variable output..
I can tell you that at this point right now, my series 7 is on Heating Speed 2, both pumps on (VS at 12%) flow is 12.9 gpm.


I don't have the specs in front of my, but from what I remember, my loop field is 5-205' long horizontal runs ~15 ft deep. I believe 3/4" in into 1-1/2" headers to the flow center (don't quote me on those)

 

So, I took some time to cycle the unit through some higher heating speeds... Here are the flows at various outputs of the VS and the constant speed pump on (because it is always on when the unit is on!)
12% - 12.9 gpm
26% - 13.7 gpm
33% - 14.3 gpm
47% - 15.5 gpm
54% - 16.2 gpm
68% - 17.7 gpm
75% - 18.6 gpm


I guess the major desire comes from the fact that the UP26-99 pulls a constant 246.1 watts, there is a savings to be had when the unit runs 24 hours a day (usually heat speed 1 or 2). If the magna geo 32-140 (VS) can satisfy the unit at 120-210 watts, that would be a good amount of savings (246.1w*24hr * 30 days)/1000kwh = 177.19 kwh/month. This doesn't seem like much, but when my usage last month 860kwh, that is 20%.
Granted, the VS pump would still account for 86.4 kwh per month at a minimum (continuous operation), I just think there is a more efficient way to run these pumps.

 

We are running the 32-140 between 16-190 watts. depending on the size and the compressor unit. Obviously 12.9 gpm is way over-pumping with a 5 ton 7 series running in first or second stage.

 

That cant be right.. Plus the Aurora web link estimates the flow center wattage.. This can be adjusted through the aid tool interface. You can change it to a variety of pumps and it will estimate wattage.
Here is the specs from geo-link

With just the magna geo, minimum wattage should be 120 watts.