condensing boiler not condensing

chris_95

tim,
originally, i was heating the zones directly with
boiler @115*. the boiler could not modulate low enough
to keep from short-cycling. hence my decision to use a buffer tank.
now the boiler is heating the water in the buffer tank instead. return water from the zones enter the top of the
buffer where it "blends" with heating water from the boiler.
as the tank water cools it falls to the bottom and is returned to the boiler for reheating. the tank's aquastat
controls boiler firing and water temp. which is now set at
120*.
the heated water in the tank goes to the system supply manifold where it is circulated to the indivdual zones.
the space thermostats control the respective circualtors.
they do not control the boiler firing rate. because of the
tank temperature, a zone can continue to draw heating water
even if the boiler is not firing! this works to much longer
firing times and also much longer standby times as well.
i could run the tank a few degrees cooler (like 110*)
but i think i'd lose some of the standby benefits.
my main concern was lack of condensate and/or causing
harm to the boiler.
sorry, i don't have a digital camera and my scanner is
broken.but if you can picture the boiler firing the buffer
tank and system return water mixing with heated water from
the boiler and ciculators drawing only from the buffer tank,
then you have the whole story!
thanks for your reply. i also welcome other views.

chris_95

condensing boiler not condensing

i have a quietside qvw9-125 that i added a buffer tank to
minimize shortcycling. there are 5 radiant zones, but none
are large enough to keep the boiler running longer than
about 2min. unless all 5 call for heat at the same time.
before adding the buffer, the boiler made plenty of condensate. with the buffer, condensate is scant if at all.
firing times have increased to 10-12min. a huge improvement!
is lack of condensate due to the much warmer return water
temps.? i'm still supplying the same 120* water as before.
now the return is "blending" with heating water and therefore not subjecting the boiler to cold water return.
is the lack of condensate harmful to the boiler?
the boiler seems happy especially now that it is firing at
much longer rates.

comments?

tim smith

Pics & a diagram would be helpful to see what's been done

Not condensing will not hurt the boiler but reduces efficiency a bit. The pics and drawing may help us see if we can get your temps down a bit so you are condensing. I wonder what you mean by your mixing down to your 120 supply temp, that sounds like you are running higher temp in buffer tank.

TimS

another way

is to connect system return to bottom of buffer tank and boiler return to bottom then boiler supply to top of buffer tank and system supply to top of buffer tank this allows the coldest water to return to boiler, the supply water stratofys and your system supply temp will be near same temp as boiler supply . I dont use any aquastat on buffer tank. try it with outdoor reset if your boiler is capable?

chris_95

gerry,
something i've noticed with my current piping arrangement....
the system supply temp. is sometimes slightly cooler
than the heating water going to the tank from the boiler.
also when a zone is still calling for heat and the boiler is in the standby mode, it seems the system supply temps.
are quite a bit cooler than aquastat setpoint. perhaps
the system return water temp. is cool enough to "pollute"
the outgoing system supply temp. which would account for
what i've been seeing in the statement above. afterall,
both system supply and return are piped to the top of the
buffer tank, although i do have a dip tube which directs
tank heating water and system return water towards the
bottom of the tank (about 8" off the bottom). do you still
think i would benefit from blending at the bottom where
the tank heating water exits and returns to the boiler?
this is good! please keep the info coming.

TimS

another way

blending at the bottom thats why your boiler return is not the coolest water thats why your system supply can be cooler tha your boiler supply. what kind of buffer tank are you using? does it have two seperate connections down low and two seperate connections high on buffer tank? I gotta get to work get something fixed today. i'll check on this post tonight.

chris_95

condensing boiler not condensing

gerry,
it's painful to admit, but i am using a 40gal. hw tank
that i already had available. very plain. 2 tappings at the
top and 1 tapping at the bottom where the drain used to be.
the tapping where the cw make-up would normally be plumbed
is now the boiler heating water and the system return water
tee'd together. the tapping where hw discharge would normally occur is now the system supply. the boiler heating
water returns to the boiler via the former drain tapping.
the tank's lower thermostat is now the aquastat which controls the boiler. i guess i was working under the assumption that the dip tube would direct the cooler system return water to the
bottom of the tank where it should blend with the boiler
heating water which in turn being hotter should migrate to the top of the tank and become system heating supply.
does this make sense? things seem to be working except
the boiler is not making condensate.

TimS

another way

Mike the 40 gallon wh is ok I admire your efforts and recognizing small problems . this will be an easy fix there should be another 3/4 connection on top it has the t&p relief valve in it remove the t&p you dont need it the boiler has a pressure relief valve already, ok now move the boiler supply to this tapping on the wh all your other connections are ok system return stays where it is already on the diptube now you'll get the coolest water to return to boiler, boiler will be condensating again and loving it. Then I'd prefer the call for heat come from your zone controller to boiler don't need the stat on the wh I think you mentioned the boiler setpoint is at 120 that should be ok. This will keep the boiler pump running and the boiler knows how todo the rest.

TimS

another way

curious about your boiler is it a QVW9 or a QVM9 dual purpose, looks interesting ? How do you like it?

chris_95

condensing boiler not condensing

gerry,
thank you for the critque on my buffer tank. i was
actually looking for an excuse to move the boiler supply
at the tank anyway. by doing this i'll be seperating the
supply from the system return water which will still be
delivered to the bottom of the tank via the dip tube. in
all honesty i'm a little concerned about this change during
the winter. when i originally plumbed it, careful as i was,
the entire radiant system was overrun with AIR! which i had
an unmerciful time purging. the rehau brass zone manifolds
i have are less than user friendly when it comes to purging.
i'd rather defer this exercise until warmer months. i have
my largest zone (6loop) in the 1st floor with the manifold
up near the garage ceiling. the other 2 are in the basement
and garage serving those areas. even using the presure-purge
technique, it took 3-4 days to get out all the air.there is
also a spriratrol purge unit on the supply manifold just
upstream from the circulators.
when i started this exercise, i was using the fr-5 stat that came with the quietside (QVM9-125 sorry) but quickly found it was not controlling firing times to my liking. it was getting it's signal from the zone controller. i feel my best temps. and firing times are coming from my present set-up. with the fr-5 they were less
less often, but also of shorter duration when firing and
the supply water temp. was dropping too low. at least now,
the tank is sending out warm water consistently and not the
stone-cold temps. as with the fr-5 set-up.
i'm finding this info tremendously interesting! i feel
the more we share, the more we learn.
thanks

chris_95

QVM9-125 quietside

gerry,
sorry about the confusion on the boiler model.
this being my 1st condensing boiler, i have nothing to
compare it with.
that said, i think it's a marvelous heating unit.
it has 2 seperate heating sources. 1 for dhw, and 1
for space heating. the dhw side has its own heat exchanger
which has priority over the space heating. i'm using it to
fire an indirect storage tank for dhw. actually, i used
the plumbing arrangement of the dhw tank as a template for
the buffer tank which we've been discussing. once again,i'm
using the lower stat in the dhw tank to activate a taco
circulator which in turn closes a flow switch inside the
quietside and starts the dhw heating process. so, not wanting to re-invent the buffer tank, i duplicated this
plumbing set-up almost exactly, except w/o the circulator.
with the exception of my fears about non-condensing
i think the quietside has been a very good heating source
thus far. it's now in its 3rd season.
i guess if i could suggest any changes to the design,
it would be to offer a smaller modulating gas valve to get
down in the 25-30,000btuh output range.unfortunately, i
think 46kbtuh is as low as any quietside goes.

hot_rod

a good purge option

Is shown in this drawing. It allows a good, complete purge of all points of the system. With rdiant, try purhging just one or two loops at a time. you may not have enough flow to purge the entire manifold at one shot.

The Caleffi fill valve is excellent for filling an purging as it is a fast fill valve. set it at 25 psi for fast purge, then lower to 12 psi set.

Is your buffer an electric tank? if so use the element holes as the buffer connections. Larger diameter and it uses the tank better than the top connections.

You can also tee together the top two connections (dip tube removed) for increased flow.

hr

Unknown

Buffer Tank

Mike I am attaching a pdf file on using a water heater as a buffer tank, unfortunately I dont know how to copy just the single page. It is a installation manual on a geothermal unit ( page 19 to 21) but will apply to your situation. Hope this helps.
TONY

gerry_6

please clarify

Mike what is a fr-5? I'm also confused how you have connected the quietside boiler? I'm not familiar with the quietside just been checking it out on the web.
it has 1/2" connections for dhw I think which is flow switch activated ,flows thru the plate hx. Has 3/4" boiler supply return connections and a internal pump I think.

chris_95

> Is shown in this drawing. It allows a good,

> complete purge of all points of the system. With

> rdiant, try purhging just one or two loops at a

> time. you may not have enough flow to purge the

> entire manifold at one shot.

>

> The Caleffi

> fill valve is excellent for filling an purging as

> it is a fast fill valve. set it at 25 psi for

> fast purge, then lower to 12 psi set.

>

> Is your

> buffer an electric tank? if so use the element

> holes as the buffer connections. Larger diameter

> and it uses the tank better than the top

> connections.

>

> You can also tee together the top

> two connections (dip tube removed) for increased

> flow.

>

> hr

chris_95

radiant purging

hot rod,
thanks for the drawing, i need to study it awhile.
as for my present purging technique, i use a garden
hose and house water pressure (60psi) to do the work.
rehau pro-balance manifolds are brass units with an
isolation valve at one end and a combination vent valve and
drain valve at the opposite end. the return manifold has
small metering cocks, 1 for each loop, about the length of
the manifold to permit balancing and/or isolating a loop(s).
my method is to attach the garden hose to the drain
on the supply manifold, close its isolation valve, and then
shut off all but 1 of the balancing cocks on the return
manifold.with a drain hose attached,i apply house water pressure to the supply manifold. i insert the drain hose into a bucket of water and watch for expelled air. when the water in the bucket is no longer showing bubbles, that loop is probably purged. continue on with each cock until that return zone manifold is air-free. to do the mains running to each manifold, i basically do the same thing, except the pressure
is introduced back at the system supply and return manifolds. this was the method taught me by the installer.
anyone see any problems purging this way?

chris_95

quietside QVM9-125

gerry,
excuse me for my poor description of the boiler.
on the heating side, the boiler heats water for the
buffer tank thru 3/4" supply and return connections. the
boiler has its own circulator inside.this assembly is
heating the water for the buffer tank only. on a call for
heat from the buffer the boiler's circulator starts up,
the pre-purge cycle for the burner commences and boiler
water heating begins once the burner lights off. btw, the
3/4" connections run over to the buffer tank tappings at 1
on top (former hw tank COLD) and (former hw tank drain
on bottom). this is the supply/return arrangement for heating. this heated water leaves the buffer and goes to the radiant system manifold w/ zone circulators attached.
on the dhw side, the boiler's burner does a similar
dance except dhw is made in a plate/plate hx which keeps
heating water and dhw seperate and potable.dhw leaves the
boiler hx by 1/2" connections and goes to an indirect water heater which i mentioned earlier. the taco circulator runs
dhw thru the plate/plate hx. this is what's so cool about the quietside unit. no tempering valves,etc. by using the tank's lower stat, it's just like using a conventional hw tank with the addition of a stat-controlled pump.
gerry, i do have some thoughts on our earlier discussion of the buffer plumbing. if i introduce heating
water form the boiler into the former t&p location won't
that be short-circuited directly to the radiant system
supply and never really heat the water in the tank and
re-create the short-cycling which i'm trying to eliminate?
afterall, the former t&p tapping and the hw discharge tapping (which is now the system heating supply) are only 6"apart and both flush with the underside of the tank head.
correct me if i'm wrong, but it seems better mixing of
system return water and heating water will occcur at the bottom of the dip tube, not ideal but at least heating buffer water.
thoughts?

chris_95

fr-5 quietside package

gerry,
i forgot to mention.
the fr-5 is part of the quietside microprocessor
package. it can be used as an air temp sensing stat for
a single zone heating application or it can be switched
to a water temp sensing stat which tells the boiler what to do. it works well when the boiler is running barefoot,but
when i attached the buffer tank, it seems to create poor
temperture control and turn the boiler off prematurly in
my opinion.
i believe it is also on the accompanying quietside
website.

chris_95

quietside and lime conditions

something else has been bothering me. this house is about
3yrs. old. the lime deposits on the sinks and fixtures are
much more prevalent than what i experienced at my old home
less than 1/4mile down the street. both residences are fed
from the same water main.
is the quietside dhw heat hx somehow causing this increase
in lime deposits. i don't see how since the dhw at both
locations comes from a hw tank and not directly from a
heat hx.

gerry_6

hydraulic seperation/buffer tank

http://www.pmengineer.com/Articles/Article_Rotation/BNP_GUID_9-5-2006_A_10000000000000166945

Mike this should clear it up hope it motivates you too.
http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_1_us.pdf


I apologize for all the reading material , figure 9,10,11 on pages 8,9 shows how the mixing happens depending on how many or few zones call for heat, this is what you can do with your buffer tank.

Enjoy , Gerry A