I have been thinking for a while about putting a time delay relay on the circulation pump so that after the system shuts off it will continue to circulate the water for maybe 15 minutes or so. Anyone do this before? I'm looking for a relay that would do the trick as well. Any info is appreciated, thanks!

 

There are several controls available to do what you are looking to do. What kind of zoning do you have? Pumps, zone valves w/ or w/o end switches? How many zones? More info is needed to make some recommendations.

 

I'm not real good at boilers, but is it that yours is set up for a cold start and you want the circulator to run the awhile longer after call is completed to utilize some of the heat left in the boiler?

Just trying to understand the purpose for the delay.

Bud

 

I've got no zone valves, so it was easy... if you have valves, you need some way to keep them open, but:

A strap on aquastat on the supply pipe... wire the make on rise contacts across the circ relay contacts in your aquastat will work.

I've got the aquastat set to close at 140, and about 20 degree of diff so it shuts off at around 120 or so...

works great!

 

With a boiler high limit control this will cause an overshoot on the zone. IOW, it gets too hot in the living space.

Now, if an ODR is in place then a post purge on the boiler water helps. Although it also depends upon the type of radiation. It can be better to purge to another zone then the one that last called for heat.

Al.

 

True that...

I should add that many of today's thermostats will 'adapt' the anticipator setting to compensate.

After a few heating cycles, my Honeywell t'stat 'learned' that the room was overshooting slightly and shortened the anticipator setting. Before I hooked this up, the burner would routinely fire the water up to 160-165 before the t'stat satisfied. Now, it's not uncommon for the burner to shut down at 145-150.

 

Post purging into an indirect water heater or buffer tank is sweet.

 

You can find all sortf of electronic relays online at Graingers - see Time Delay Relays - Relays - Electrical - Grainger Industrial Supply. I was, at one point, looking for a relay that would allow a pump to run only for 3 minutes (to overcome a static head issue) and I found one at Graingers, but my relay became unnecessary.

There are all sorts of relays (time-delay-turn-on, turn-on-for-only-a-bit, etc.) and I'm certain that there is one for you, if you can find it. Many of the relays perform multiple functions, and all of them require a special socket (much less expensive than the relay) that must be wired properly in order for the relay to function.

Good luck,

Jeff

 

You guys know that I play the devils advocate but I am still gathering info about post purge on pumps. Just trying to get my arms around this. Every time I think I totally understand it something else comes up that makes me rethink it.
Trooper, did you ever check fuel consumption with and without post purge pumps. I assume since the thermostat has intellegen recovery the system works at a lower temp and therefore saves money. What type of radiation do you have? How many zones do you have? How did you come up with the 120º and not something lower or higher?
Are you familiar with the old two-stage thermostat operation? Would that make sense as opposed to post purge? I totally agree with 2 stage stats and feel it is a great idea that could save many fuel dollars with a simple application.

 

rbeck, I do have data from the 'old days', but it can't be relied upon. Summer '06 was the year we found the underground fuel tank leaking. I have no idea how much it was leaking, and since then, of course my fuel consumption has gone down. I installed the post purge that following winter 06-07. So there's really no way to tell how much of the savings are from the PP, and how much from not spilling oil into the aquifer. Judging by the size/depth of the excavation, it's a good bet that the tank was leaking a lot, and for a long time...


[by the way, this is not the full size of the excavation... it eventually went about four feet deeper, and about 20 more feet to the right of the pic, all the way to the end of the garage]

Mostly fin-tube baseboard. Cabinet convector in downstairs bathroom, and in kitchen (both on monoflo's). One zone, two loops, upstairs and down (appx 2000 SqFt) [pics above don't show house, but attached shop/garage, house is to left].

I just picked a temp for the lower end. I guesstimated that letting it go down to 120 would be near the point of diminishing returns... the upper end I messed around with a bit. Started at 160, but during the shoulder seasons the temp would mostly not get that high... so lowered it until I found a 'sweet spot' that seemed to run the post purge nearly every heat cycle.

No I'm not... I would be willing to experiment though if you knew of a source for new ones!

Do tell how they work? Does one stage run the pump, and the other the burner?

 

I didn't mean to 'drift' the thread, but I can never resist bringing up the 'Big Dig'... so forget about that, and we'll try to stay on the original topic of 'Time Delay Relay' or "Post Purging"...

 

This idea is about 30 years old.You are absolutely correct. Stage one runs the pump and stage 2 operates the burner. I guess this is more pre-purge and post purge. Testing was done by University of Illinois this idea many years ago. They actually gathered test data for more than 10 years. They claimed you can save between 15% - 25% dependent on the installed radiation. The more over radiated the home is and the more water volume the higher the savings. It actually works better with multi-zones.

In a single zone system the pump comes on and than the burners and back to stage one and we get post purge.

When the thermostat calls the pump comes on and if the thermostat drops 1 degree the burners come on. the advantage with multiple zones is let's assume zone one is calling and the burners are firing, a second zone comes on to stage 1. Zone one satisfies and zone two is still on stage 1 and the burners may not fire. this is not a great idea for mod/cons as water volume works better.

With testing we were involved in we found out during most of the winter when the system water temps get down to about 120f to 125f the pump stays on and the burners do not fire for about 20 minutes. This was done with cast iron baseboard. It just seemed to hold it's own for quite awhile. This is another case where thermal transfer, thermal storage and water volume is a plus.
The test home had an old boiler in it. We replaced the boiler with a properly sized cast iron boiler and the fuel savings was about 31%. The following winter we did the two stage thermostats and saved another 18%. I believe copper tube baseboard would be lees savings bit cast iron rads would be more savings. It is great to be able to do these studies for fact finding info. I guess we need to do some testing on circulator post purge.
A good test on your home would be constant run pump with the thermostat just operating the boiler unless you make domestic hot water with the boiler. An hour meter would be interesting to see if it changes the operating time of the burner.

 

Hi there.. my8950 :

I was reading your thread and the advice from others. Great to have good advice- here is more... I also have a house 100+ years old in Pennsylvania with a one zone system, oil furnace and hot water (hydronic) heat with a two pipe circulation system. High limit is set at 190; low limit is 130 with a 25 differential. Honeywell L8124 Aquastat.

My boiler fires and the pump sends a surge of hot water; the pump stops while the burner heats the next batch, then when it comes to temp the pump kicks on and away it goes as another surge of hot water to radiators. The thermostat comes up to heat and shuts off the burner and pump before all the radiators are refreshed with the hottest water. Out of seven cast iron radiators, what I am left with is four "HOT" radiators and three "COOL to barely warm" radiators. So, what the water needs to be pushed more to get out to the farthest ones so they all get hot..

I found these two products online and I am getting prices on both. :

Do a Google search for TheSmoother.com What it does is mix the hot water by keeping the pump circulating the water after the burn cycle ends- this gets all radiators the mix of hot ambient water and they all get within 15 degrees of the same temp being circulated. It is a Canadian company. I called local HVAC plumbing supply stores and they knew nothing about this product NOR could they recommend anything similar. They just said to, "go to Radio Shack and but a delay relay switch". Maybe it was I was wearing a necktie... I can post again when I get a price on the Smoother.

Another AWESOME product (I fear will be very expensive) I found was from Beckett. It does everything the Smoother does and more. This is a brand new product and may be hard to find . Do a Google search for: Beckett AquaSmart boiler control. I called the HVAC supply today to get a price on this too- the largest HVAC supply store chain in our area EPSCO never heard of this product either...

I hope this helps you. I can let you know what I find out on both of these products.

Beer 4U2
Brian

 

AquaSmart:

Patriot Supply - 7600A0001U

Al.

 

That's an interesting control... and it includes a 'circulator hold on' feature which OP was looking for, and what my added strap-on aquastat does... ALSO, has adjustable differentials on both the HIGH and LOW limits... (low limit can be disabled if not needed, i.e. no domestic tankless coil)...

AND, something very interesting... there is a distinct DIFFERENCE in the HeatManager that is built into this unit... it appears from the literature that it is now a TRUE RESET control! Instead of only affecting the differential... it seems that it will now actually RESET the HIGH LIMIT...

Interesting! sounds like someone was listening!