Spirovent "before" the boiler on a wall-hung?

GW

Hey gang, I have always installed spirovents after the boiler on a wall hung, in other words on the hot side leaving the boiler. Last week i had this pesky BB system, I had no idea why the air just kept coming and coming, and the boiler locked up about 4 or 5 times...it was simply getting slugged with air (yes, I know how to purge zones!). I may have been getting kicked around by the existing TFI water heater (maybe air was hanging out in the tank). Anyway, i am thinking it may be better to install the spiro before the inlet of the boiler rather than the traditional supply side. Breaking tradition is not what i do all the time, please share your thoughts. Gary

Steve Whitbeck

air locked

I also install Munchkin boilers - BUT i always install the pumps with check valves (Grundfos) on the inlet side of the boiler so that air can't get traped under the check valve and inside the pump thus cavitating the pump. Since I started doing it this way I havn't had any problems. I don't like spirovents. They may get all of the micro bubbles but they don't get rid of the big bubbles very well at all on initial startup.

Steve - BELTLINE HEATING

kcopp

What wall hung......

was that?  I have had one make/model that was doing that too. They changed the boiler vent to a cheap piece o' junk instead of the Calefi that was on there. I stuck an air scoop on the etuen... problem solved.  As long as it is in there somewhere.... kpc

SpeyFitter

Pictures?

I would really love to see some pictures of the system you have an issue with.

Is it a Primary/Secondary system? Or a single pump parallel type system?

For the record, I will ALWAYS install my air seperator on the outlet of a mod-con where the temperature is highest and pressure is least (in theory anyways).

But again I'd love to see pictures.

Also, I don't expect any air seperator to get the majority of the air out. Carefully selected purge points with associated valves versus the location of the fill point combined with some time purging, will get a significant amount of the air out of the system. Then when the system is fired up for the first time, if you got time, if you can run the circulators without the heat source on if you're anal, but failing that a few air bubbles that the system circulates around as it is working to the air seperator will typically get all the air out quite quickly. Positioning of purge points, isolation valves, check valves, and fill point as well as point of no pressure change, and pumps, is CRITICAL to a system in not experiencing air related problems. If you can read some of Dan's books a few times, you'll start to see the relationship everything has to each other and how it can work for you, or against you, in the removal of air, as well as protecting critical parts of the system such as a low mass heat exchanger.

hot_rod

best at the highest temperature

point in the system. But air eliminators will work in other locations. With mod cons running radiant only they may only run 100F or so supply temperatures.



So that high temperature point in the system ain't what it use to be



This is another reason to use a good microbubble type air eliminator. They will scrub out the smallest of bubbles and even entrained air that you don't see.



Properly located Webstone valves make the initial purge and flush easy and efficient. The air purgers take over from there. Remember they all are multi pass devices. No purger gets all the bubbles on the first trip around.



hr

Jean-David Beyer

How low can a microbubble eliminator temperature go?

My boiler runs at three temperatures. 170F for the indirect hot water heater.  134F for the baseboard zone. 120F for the radiant slab zone. The contractor folowed the manufacturer's installation manual exactly as far as piping the boiler, although where it said 1" minimum, they used 1 1/4"



That system uses primary-secondary piping where the boiler is in the primary loop, and the two heating zones are in the secondary loop. The indirect is across the supply and return in the primary loop. The air eliminator, a Taco 49-125, is in the secondary loop soon after the hot supply pipe comes into the right-most T of the closely spaced Ts. So really, the separator never sees water over 140F, and that very rarely. I know the eliminator works because I could hear it hiss when some water had to be drained from the system, and then refilled.



But I may have a little air in the system, and do not know why, if I do. It cannot be very much because both zones heat just fine. The expansion tank comes out the bottom of the eliminator, and the circulators in the secondary loop come after the eliminator, so after the expansion tank (pumping away). The eliminator can tolerate 5 feet per second through it, and that is 1 1/4" pipe with two Taco 007-IFCs coming off it. A lot of the time, only one of them is running., so the flow rate should be pretty small.



Does anyone know what the minimum temperature is for these air eliminators? I am sure it is not a sharp cutoff, but how many passes should it take? According to John Siegenthaler's book, I infer that two weeks should surely be enough, but it does not seem so. I do not know what temperature he had in mind, though.

SpeyFitter

Don't worry about it!

I wouldn't worry about the minimum temperature in your system relative to your air eliminator. The reason you want the air eliminator in an area where there is the warmest or hottest water is because cold water tends to entrain or encapsulate (if that's the right terminology) air better than warm or hot water does, so if you put the air eliminator in the area of the warmest water, you are working with the natural ability of air to seperatore from water as the temperature increases.  In your system, as long as you're not pumping towards the air eliminator, and as long as your expansion tank is close to your air eliminator, you should be fine.



I know this because I used to work several years ago at a Salmon (Fish) Hatchery. We often took oxygen samples during our various fish culture activities for obvious reasons, and when winter came around the cold 34-36 F degree water had much higher oxygen levels than the 60-65 F degree river water in the Summer.

The key is to TRY and put the air seperator near the area of the warmest water (if possible) and the area where there is the lowest pressure. This means it's often a good idea to pump away from it. In a P/S system, pumping away means you pump into the boiler on the primary loop and the air eliminator is on the outlet of the boiler (supply) side; most of the boilers head will (or should have) dissipated through the heat exchanger to the extent that you end up with an area of the lowest pressure and warmest temperature in the outlet of a mod-con.

An alternate location is on the secondary loop of the radiant system which sounds like your system. Since your indirect loop and other loops do not contain a lot of water, they are much easier to purge if proper purge points are set up. So you should be fine. My opinion though is the best place for an air seperator is on the boiler primary loop on the outlet of the mod-con - basically the same location as on a conventional boiler.

I won't always tie my point of no pressure change into the bottom of the air seperator tapping though. Sometimes it's advantageous and saves you a piping headache to pipe the point of no pressure change to a tee right near the inlet of the boiler primary pump comibned with the main drain down AND the relief valve if it's not built into the boiler cabinet. This makes piping a little simpler sometimes, depending on the boiler.

hot_rod

temperature and pressurre

Henry Law. Air separators are also used on chilled water systems, so low temperatures seen in radiant are not a problem.



This pdf has a graph to show the temperature/ pressure relationship and how air removal works.





www.caleffi.us/en_US/Technical_brochures/01060/01060.pdf

GW

thanks for the comments

it's a Viessmann vito 100, as far as 'wall hung" we pipe them all the same, with a boiler pump and a close-space tee, we have the spiro on the supply side, my question is have you ever put it on the return side. Technically it would still 'pump away' because of the boiler pump. gary

kcopp

I guess the ....

answer is yes. The boiler I had the air lockout w/ was a Embasy Onex. The boiler design got an  air bubble stuck in the top and the air vent wouldnt let it out. The air scoop (no extrol) on the return helps. The circ and the expansion tank are both on the boiler since it is a combi boiler. kpc