why does Munchkin need P/S piping?

R. Kalia

I am a homeowner trying to figure things out in preparation for a fall boiler purchase.

The way primary/secondary piping is described on the web pages I found, it is to warm up the return water so as to prevent thermal shock or condensation. But this does not apply to a Munchkin w/Vision. So why does it need P/S piping?

Is it ONLY to maintain full flow through the low-mass boiler? If so, if I have the circulator set to run ALL the time (cut off only by the main power switch to the boiler) I should not need P/S pumping...right?

Do I always need one more circulator for a P/S system compared to a traditional system? (Since circulators draw some current, this is an energy issue, although admittedly not a huge one. A small primary circulator might use about $5 worth of electricity a month.)

J.C.A._3

Yes, the reason is FLOW!

As to 5.00$ worth of electricity for a month, time for a revise of that. Maybe 5.00$ per year. The power consumption on the recomended (water lubricated) pumps is minimal.

Water sitting too long will cycle the burner up and down too much, go with the recomended piping diagrams! Chris

Guy_5

P/S Piping

Primary/ Secondary piping is suggested when piping the Munchkin in order to maintain a minimum flow rates through the heat exchanger. It also reduces the possibility of velocity noises in the system due to the necessary flow rates. You need not worry about the circulator running continuously, as the pump will NOT be energized unless there is a demand for heat (or hot water) put onto the boiler.

R. Kalia

power

I looked up B&G's smallest water-lubricated pump, the NRF-9F/LW (the LW is for low watts). The B&G catalog page:

http://fhaspapp.ittind.com/literature/files/1613.pdf

says it draws 41 watts. That's 1 KW-hr per day, or 10cents/day in my area (10cents/KW-Hr is the average rate after all taxes and fees). That's $3/month, less than $5/month, but not $5/year either---in my area the heating season is 8 months so that's $24/year.

The bigger secondary pump (say NRF-33, 130 watts), will also now run continuously rather than intermittently because of outdoor reset, so the additional cost for pumping may be about $75/year, which in my case is 5% of the annual $1500 gas cost. That cost doesn't appear on the gas bill, so homeowners may think they're saving 5% more than they really are.

R. Kalia

reset = pump runs a lot, no?

> You need not worry about the circulator running

> continuously, as the pump will NOT be energized

> unless there is a demand for heat (or hot water)


But I thought the whole point of a modern hydronic installation is that the water should run all or nearly all the time. What I've been reading is that one should avoid a 'bang-bang' system.

Dave Yates (PAH)

P/S not always needed!

If you have a system with adequate flow and it's a single zone, then P/S won't be necessary. However, utilizing a primary loop gives me the ability to provide the Munchkin with exactly what it wants to see where flow is concerned.

We use P/S pumping on all of our Burnham boilers too.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mike T., Swampeast MO

Are Munchies similar to some others

that require a "low-loss" header when connected to the essentially non-existant head loss of a converted gravity system?

Unknown

Munchies and Flow

Because of the tiny heat exchanger there is a REQUIRED flow across ALL low mass boilers. Whether a copper fin or a SS tube or tiny CI, low flow would BOIL the water.

In the Munchie/Pinnicle there is a pressure switch that need to have a constant pressure, on Lochinvars there is a pressure switch.

All of these require primary secondary in order to make sure there is proper flow (yes to much flow is almost as bad as not enough).

Also, as mentioned earlier, with primary/secondary pumping it is easy to do system supply water temperature reset.


wheels