Head pressure high for snowmelt slab! What pump?

Tcatflyer

I've installed a snowmelt system in a slab on my house. Looking back I should have used larger PEX. So now I have 1/2" SDR 9 type PEX in 15 loops. Those loops are 290 ft long. This calculates to roughly 25 PSI (58 ft head) of pressure drop. When I add in the PHE and misc fittings and pipe it approaches 33 PSI. I'm planning on having flow rates of 2 GPM in each loop to ensure turbulent flow (30 GPM total). It appears this puts me out of the range of typical quiet low electricity consuming circulator pumps. I'm thinking the pump I need is going to sound like an air compressor is running but so be it.

Anyone suggest a reliable pump with 30 gpm @ 33 PSI?

Other info:

150 BTU/hr/sq ft in slab
270,000 BTU total load (1800 sq ft slab)
20° delta T
50% propylene glycol solution for North Dakota installation
3.62 ft/sec solution velocity

Thanks, Darin

Hot_water_fan

Ha! Which calculator did you use?

For parallel loops, you add the flow but do not add the head. 

There’s no way you need 2 GPM per loop for turbulent flow.

hot_rod

Here is a 300’ loop at 2 gpm with 50% glycol.

Keeps you just under the 4 fps velocity.

Your probably looking at this type of pump for that head

GroundUp

You will never get anywhere near 2 GPM through a 290ft loop of 1/2" with 50% glycol. Cut your expectations back to .7-.8 GPM with a 50 degree delta and use something like a Grundfos 26-99

hot_rod

I made this exact mistake early in my hydronic career. My Grundfos rep sized a pump like I pictured above. You can usually pump your way out of a poor design and salvage it.

We serviced that "vacation home" for many years and the system did melt as designed.

A small improvement would be to cut back to a 40% glycol. It drops you from 75 to 67' head on a 300' loop

Tcatflyer

hot_rod said:

Here is a 300’ loop at 2 gpm with 50% glycol.

Keeps you just under the 4 fps velocity.

Your probably looking at this type of pump for that head

Yup, that's the same calculator I used.

Thanks for the pump suggestion. Today a rep from Taco suggested using a higher delta T and being satisfied with 0.8 GPM.

He did say there's a pump that can do 2 GPM with the glycol solution but it's not going to be quiet or cheap to run. I don't really care about the cost of electricity because it's only going to be used for snomelt.

Thanks, Darin

hot_rod

I suppose it depends on how critical it is to get full output. Slower flow will reduce the warm up, and limit the melt ratio. Is it a steep or dangerous drive way? Accessibility concerns?
For a residential system, maybe that it is not a big deal cutting down the output. How much snow do you generally get?

As for electrical consumption, snow melting in general is an expensive proposition.That pumping load will be the least of your concerns when you heat the great outdoors🤓

Start with the small circ, you could always series a second to double the head if you really want the extra fizz.