Grundfos Alpha and 1/4" tubing

Andruid_2

I'm wanting to replace an old Grundfos 26-96 with a pair of Grundfos Alphas. The system being fed is a radiant slab with the old 1/4" black rubber tube...6 manifolds with zone valves. I'm not real solid on knowing what happens when the Alpha is trying to maintain constant pressure, and the tubing it's pumping into is restrictive by its nature. Does the restrictive tubing confuse the Alpha logic? Could someone please help me understand?

Thank you

Zman

The auto adapt will not like the 1/4" tubing. The other modes probably won't care. Can you sketch out what you are proposing. Which alpha did you have in mind?

Derheatmeister

Hmmm 1/4" tube = Approx. 6mm Tube. Is this a Stapled up Dog bone type tube ? I have not seen this tubing in years... It is very restrictive and this is not a common size tubing in Europe..I don't think that the danish engineers would considered this since the market does not support it.
Also..Pairing up alphas is not recommended..They may play Drunken ping pong unless they are hydronicly separated (Cannot see each other,flow wise)
Piping schedule/schematics would be helpful.

Andruid_2

I use Alpha2's. I typically use the "constant pressure" setting instead of "Auto Adapt".

It took me a moment, but now I understand "dog-bone type tube". Yes, it's that, but it's in a slab-on-grade downstairs and a thin-slab upstairs...approximately 7-8" on center.

I apologize for not sketching the piping. It's really basic (I've attached pics)...pump out to 6 parallel loops, back again, through a plate heat-exchanger, and pumped out again. I intend to split the loops between 2 Alphas. [I'm referring to everything to the left of the boiler and plate exchanger]

kcopp

I understand you wanting to save some electricity.... If it is working now I would keep it as is. Furthermore the Grundfos that is on there is a Bronze circulator. They dont make Alphas in bronze.

Derheatmeister

Electric Boiler..Hopefully your KW rates are low otherwise this may cost alot to operate..
Not sure about a couple things
1. Is your current circulating pump made of Cast Iron and what's the model
2. In which direction is the current circulator pumping..Up or Down.
3. What is the model and function of the Tekmar control.
4. Do you have a problem with the Tubing ..Oxygen Ingestion,Corrosion,Sludge build up in the circ,Poor heat transfer,Some of the rooms not keeping up ?
The reason i am asking about the tubing is because we used to see these problems associated with this tubing and i hate to see you "waste" time and money on 1 Grundfos Alpha2 26-99 F due to the inherent oxygen problems.

Andruid_2

I didn't know Alphas are not available in bronze. That's important as the rubber tubing side of the plate exchanger requires that (or stainless steel).

Electricity isn't relatively cheap here. They were looking for an air to water heat pump because of thousand dollar a month power bills.

I agree that the rubber tubing is a problem. I saw 40°F delta tees while there and suspect there is some flow issues due to degraded tubing.

I have gone ahead and recommended that they not dump a bunch of money into a possibly failing system, which is really sad because radiant floors are so wonderful. I suggested installing a savvy mini-split system, if they want to reduce their monthly power bill.

hot_rod

Looks like Bio Energy Solar or Radiant-roll tube, a basic EPDM tube with no O2 barrier. Typically they were 150' loop lengths, and even still required a high head circ. The Alpha 26 99 would be an option, I believe a stainless version is available. I'd run a cleaner and flush that old tube also. Most often the tube dries out and splits at the manifold from UV breakdown, be carefull if you mess with the manifolds . The tube in the slab can last 20- 30 years or more if nothing moves and shears it.
Ideally the entire system would be non ferrous, or use a plate HX to separate the tube from the steel boiler, tank, etc.

hot_rod

Ooops, looks like it does have a HX isolation already, good!