Heating and air conditioning - Boiler loop question?

Author

Boiler loop question?

John Katic

2006-01-09, 10:21 pm

On a BW9 gas boiler (same as Quantum 90 or Dunkirk) there is an option to
install a small primary loop pump which activates the flow switch and is
on all the time. Then to install a large Armstrong pump on the secondary
loop which is on only when there is a call for heat from the thermostat.

or

to install one large armstrong pump on just the secondary loop (no
primary loop) which is on all the time. The thermostat just turns the
boiler on.

With a cast iron rad system which is better? more efficient?
The BW9 has a 2-3 gallon cast aluminum boiler.

thanks in advance

GOJONESatCOMCASTdotNET

2006-01-20, 10:21 pm

Both work, & in recent years many boiler mfgrs have revised they're piping
layout.

With condensing/modulating boilers, that operate off water temp & condense
with cooler return water, for peak eff,
running the larger pump & having a larger volume of cold return water will
cause the boiler to condense longer &
operate at a higher efficiency. In this case, the modulation looses some
effect as the boiler is forced to max output to meet the load.

A smaller primary loop feeding the larger loop makes sense with a cast iron
non condensing boiler as it would insure
a return water temp above 120dF to avoid condensing & corrosion.
Usually on primary/secondary systems you maintain the primary loop at a
higher temp & draw off this loop to
heat up the secondary. With modulation the boiler can idle down to a lower
temp on the primary loop & deliver the btu's as required.

The question is which cost less to operate, a single pump on 24/7 & cycling
the boiler on a heat call,
or a small pump operating on return water temp & a large pump only on during
a heat call.
(Although I can't see a reason to run the primary loop when there is no call
at all.)
My preference small primary/ large secondary.
But I've been wrong before.

good luck
sloyal
st.paul,mn.

"John Katic" <aq073@FreeNet.Carleton.CA> wrote in message
news:dpv2r0$k40$1@theodyn.ncf.ca...
> On a BW9 gas boiler (same as Quantum 90 or Dunkirk) there is an option to
> install a small primary loop pump which activates the flow switch and is
> on all the time. Then to install a large Armstrong pump on the secondary
> loop which is on only when there is a call for heat from the thermostat.
>
> or
>
> to install one large armstrong pump on just the secondary loop (no
> primary loop) which is on all the time. The thermostat just turns the
> boiler on.
>
> With a cast iron rad system which is better? more efficient?
> The BW9 has a 2-3 gallon cast aluminum boiler.
>
>
> thanks in advance
>

John Katic

2006-01-23, 12:21 am

"GOJONESatCOMCASTdotNET" (steven.l.jones@comcast.net) writes:
> Both work, & in recent years many boiler mfgrs have revised they're piping
> layout.
>
> With condensing/modulating boilers, that operate off water temp & condense
> with cooler return water, for peak eff,
> running the larger pump & having a larger volume of cold return water will
> cause the boiler to condense longer &
> operate at a higher efficiency. In this case, the modulation looses some
> effect as the boiler is forced to max output to meet the load.
>
> A smaller primary loop feeding the larger loop makes sense with a cast iron
> non condensing boiler as it would insure
> a return water temp above 120dF to avoid condensing & corrosion.
> Usually on primary/secondary systems you maintain the primary loop at a
> higher temp & draw off this loop to
> heat up the secondary. With modulation the boiler can idle down to a lower
> temp on the primary loop & deliver the btu's as required.
>
> The question is which cost less to operate, a single pump on 24/7 & cycling
> the boiler on a heat call,
> or a small pump operating on return water temp & a large pump only on during
> a heat call.
> (Although I can't see a reason to run the primary loop when there is no call
> at all.)
> My preference small primary/ large secondary.
> But I've been wrong before.

Hi Steven,
Thanks for your input. The BW9 (indentical to the Dunkirk Quantum 90) is
a 90% high efficiency condensing cast aluminum boiler. It does not
modulate and is bolier temp reaches a max of 140 deg F. The high temp
aquastat is set at 165 deg F. This is adjustable... and can be set lower
during the fall or spring.

The manual for the Quantum 90 (BW9) does not show a primary loop but it
comes with a small Taco pump. The installers here normally want to intall
a large seconday pump running 24/7 during the heating season which closes the
flow switch and a small primary loop pump to come on heat there ia call for
heat. With a one loop system for the circ pump to start with a call for
heat they said they have to install a relay between the flow switch and the
boiler.

In my case the boiler is designed to condense (does not modulate) so a one
loop system makes more sense to me. And the main circ pump should come on
with a call for heat and shut off at the end leaving the heat in the rads.
If it continues to circulate the cast iron rads will cool off faster.

I just want a heating system that is efficient and simple to maintain.
The old system was a gravity fed cast iron oil fired boiler that was
installed in the early 1960's.

thanks
John

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