Problem with aquastats and heat cycles

Dan_15

Hello, I have a couple of problems with my aquastats; I am hoping that if I post some pics of my system someone may know where I should start. First problem is that my boiler aquastat is makes a buzzing noise, but only when it gets pretty hot after continuous use (e.g., coming out of standby in the morning and evening). I posted a closeup pic of the relay, and it looks like its bent out of shape. I have made sure that its free of dust and debris, but the buzzing continues. I know, I should have splurged for the Logamatic controls. The second problem is that my boiler calls for heat to my indirect tank immediately whenever I turn on the hot water, even just for 30 seconds (e.g., to wash my hands). My burner is set for 1.5 GPH so I am worried that these constant startups to satisfy the indirect zone are causing excessive fuel consumption and faster wear and tear on the burner and the boiler. Is this supposed to happen? The aquastat on my indirect tank appears to be a high limit type only. Do I have the wrong type of aquastat? I know, once again, the logamatic controls will fix all this. Thanks for looking at my pics.

Dan_15

Alex Giacomuzzi

Just Sharing Some Thoughts.........

One of the reasons a relay will buzz is that the movable arm (armature) that moves the contacts to make or break positions is not completely sealed or making a good direct contact with the armature coil. This will create a buzzing sound and if there is an air gap there, the coil current will be several times what the normal armature closed current would be if the parts sealed or came in contact correctly.. This increase in current is what is heating up the coil windings in your case I would guess. If you push against the armature with just a slight pressure does the buzzing stop?
It might just be miss-alignment or something is bent.

Regarding your DHW temps....... Your piping scheme could be part of the problem. Your DHW is tapped off prior to your air removal device and could benefit from a flow check valve just for that circuit. You may be experiencing some ghost flows between the boiler, etc. and the DHW tank.

Another opportunity is to just move the setpoint on the DHW aquastat and visually observe where the make and break points occur. I would guesstimate there should be a nominal 5--10 degres maybe more between them. This should be enough to not trigger after 30 seconds of water run time.

But ---- if you have a ghost flow, your heat maybe be moving to other points within your system and possibly even up the stack.
Alex Giacomuzzi

Dan_15

Not sure I know what you mean

Thank you Alex for your reply. Can you clarify what you mean by visually observing where the make and break points are on the DHW aquastat. This is a high limit aquastat that I have set to something like 120*. Im not sure I understand what I should be looking for. Thanks.

Steve_35

He's suggesting the differential of your DHW aquastat

may be too small.

You may be able to hear it click on and off as you move the dial. If so, just turn the dial down until it clicks and note the setting. Then turn it up until it clicks and note the setting then. If the difference is only a few degrees that may cause short cycling.

If you can't hear the contacts click just hook up a voltmeter across the leads.

Dan_15

Can you also explain

OK, I understand the break point now and I will try that when I get home. Can you also explain where exactly I may need a flow check to prevent ghost flows? If you look hard at my pics, there appears to be a flow check valve between the air eliminator and the cold water supply on the DHW tank. But that is the only flow check I see, as far as I can tell. There is no flow check on the boiler supply or boiler return to the DWH tank; although there is a circulator pump on the return side between the boiler return and the DHW tank. I dont fully understand the ghost flow. Where would the ghost flow be coming from, and how does the ghost flow affect cycling the DHW tank?

Alex Giacomuzzi

I will try...

Hi Dan:

Presently you have a green Taco flow check valve just after your red B&G air separator. This flow check appears to be for (I presume) a radiator heating system with good size supplys and returns...lines that is. That is the one flow check valve I was refering to. It would be beneficial to have another flow check in the supply line going to your DHW to stop any ghost flows between lines and the boiler. This flow check should be actually in parallel with your exiting one only piped over to the DHW. Both should be after the air separator. Your piping does not reflect this presently.

A ghost flow is water (and heat) which continues to move around a system without behind pumped in an uncontrolled manner. It moves stored heat from hot to cold via currents of water even within the same pipe at times. It could be what is cooling your DHW tank off and calling for replenishment heat in a very short period of time when you open a faucet.

Once you determine what the make and break temperature points are on your DHW aquastat, set the tank temp up to say 130 deg. f. (for the break or open contact to stop the boiler) and let the boiler bring it up to that temp. After it is up to temp, and the boiler stops, now run your laundry tubs faucet for thirty seconds. Does the boiler come on?

What is the high limit setpoint that your boiler is set to?
Are you running a cold start boiler, or does the boiler maintain a minimum temp?

Good Luck Alex

Steve_35

My gut feeling

is ghost flow isn't an issue, but then I've been wrong before and most certainly will be again. The reason I don't think it's an issue is two fold.

First, the supply into the WH appears to drop from the boiler to the WH inlet a good 18". Most times the colder object is higher than the hotter object. In this case to get much in the way of convective currents I'd expect the WH inlet to be higher than the boiler supply. BTW, you are getting convective flow in the DHW hot water line. Get a trap in there and that will help. Just 3 tees will make a big difference.

Second, I suppose it's possible to get some stray currents in the DHW/boiler piping when the space heating pump is running but from the size of the piping this system is hooked to I'm guessing you have radiators. Most likely the pressure drop on that side of the system is lower than the drop through the WH. Just doesn't seem like you're going to move much if anything there.

Finally, your original complaint was "my boiler calls for heat to my indirect tank immediately whenever I turn on the hot water, even just for 30 seconds". Are you sure this statement is 100% accurate? If so, that sounds to me like some sort of control issue. Are you sure the pump isn't running before the burner fires?

If you find there seems to be a decent differential on the aquastat, turn down the space heating t-stat and have someone run the DHW until the burner fires. Turn the faucet off and wait for the burner to shut down. Give it 10 or 15 minutes and open the faucet again. Hot only and measure the water you pull off before the aquastat makes a call for heat.

Alex Giacomuzzi

I see a slightly different flow path..... with no check valves

Regarding the pumped circuit for the radiators, with the pump being on the return side I can see the following happening:

The cool return water coming back from the radiators comes out of the return pump and could move thru one or two paths depending on IF the DHW pump has a check valve in it. If it has a check valve, the flow should only go thru the boiler, BUT if there is no check valve in that pump, the flow will split given the respective resistance of the boiler loop and the pump and DHW loop. This will send cool return water thru the DHW circuit and back into the supply line from the boiler. It will cool down the Domestic hot water in the tank, until obviously the DHW call for heat and its pump starts, then the flow will be reversed.

If the room thermostat is satisfied just prior to the dhw aquastat turning on and by chance only 30 seconds of hand washing occurs, it is possible the DHW would call. Sure this is a chance occurance, but nonetheless entirely possible.

This system has much too many opportunities for heat loss in the wrong directions.. All these heat loss possiblities exist and a few more flow checks, checks , elbows, heat loss ball checks.....etc would certainly help alot...

Alex

Steve_35

I agree there are several

things that should be done differently.

Is the WH experiencing ghost flow caused by the space heating circ? Yes, it could be, but I don't see it being significant, and as I said, I've been wrong before and can count on being wrong again.

Assuming there's no IFC in the WH circ the pressure differential between the WH supply and return when the space heating circ is running should be around 1psi if I remember my Buderus pressure drop chart correctly.

Now that I'm thinking about this that way if there was ghost flow through the WH due to the space heating circ seems like that would add heat to the WH, not take it away. If he's got the WH aquastat set to 130º and the boiler aquastat at 180º much of the time the return water would be as hot or hotter than the DHW. At least at this time of the year.

Dan_15

More information

Hey guys thank you for thinking about my system. The two grundfos circulators both have built in check valves. You are right that those big old mains used to be connected to radiators, but they were all replaced by big fin/tube convectors a while ago. Its still a pretty high mass system. I keep my boiler aquastat at 180*. Its a cold start aquastat with only a high limit setting, but I never cold start the boiler; I set back about 5 degrees at night, which means that the boiler is always pretty hot. I experimented with the DHW aquastat to find the make and break points; and it appear that the differential is only about 5 degrees. I tried bringing the DHW up to temp and then ran the laundry until it called for heat. It took about 3 minutes before the call for heat. I know Im not dreaming, I know there are other times when the DHW calls for heat very quickly after turning on the faucet. I dont understand how there would be ghost flows of cooler water into the HW tank. First, if you look closely there is a backflow preventer between the system supply expansion tank and the cold water feeder on the HW tank, so I dont see how there could be any water flowing from the system that way. Second, there is a check valve on the DHW circulator between the boiler return and the DHW return, so I dont see how there could be any water backing from the boiler return into the DHW return. It looks to me like the only exposure could be on supply line beyween the boiler supply and the DHW supply. But all the water on this side of the system should be pretty hot--much hotter than 130*. I just dont see how any cooler water is backing into the DHW tank.

Steve_35

Does your DHW aquastat have an adjustable or fixed

differential? If it's adjustable you could open it up a bit.

I'm sure there are times when the burner does come on right away. There are also times the WH is calling for heat before you started using water and the circ was running but not the burner. Then the burner starts. It may only run for a minute but the circ may have been running for a couple of minutes before that.

The aquastat making a call for heat doesn't mean the burner will fire immediately. The burner will only fire if there is a call for heat and the high limit in the boiler aquastat is closed.

Dan_15

Unfortunately, I believe that the DHW aquastat is just a fixed differential; there doesnt appear to be any way to change it. Its just a cheap Honeywell aquastat. Do you think that the logamatic controls will help the system handle DHW calls and space heat calls more efficiently? Thanks.

Alex Giacomuzzi

My Goodnight Thoughts...

Hi Dan:
I must admit.... you certainly want to get that "Logamatic" real bad and maybe you should. I do not know a thing about them.... sorry no comment there.

Regarding the info. that you have provided, it appears that run times are a major concern to you and I understand that. When you are running 1.5 gph --- you are inputing over 200K into your system. Do I have that correct?? What is the design needs of your house? How many BTUH?

At 200+K input, you can make 4--5 gpm of hot water continuously. Where I am going here is -- do we have the right fit. For example, when the DHW calls, how long will the boiler run before the call is satisfied ---- assuming a worst case condition that you stop drawing water after the call is initiated. How many minutes? Next question..... on a design temp day, how long does the boiler take to satisfy the call? On a mid season day..... how long to satisfy the call? This all reflects on the cycling of your boiler. Depending on the answers to these questions, maybe a nozzle change would be in order and would provide more boiler up time and accordingly reduce the cycles without compromising anything else. You may get the operational results that you are looking for.

Given this DHW situation that we have been discussing above, you have determined that sometimes the unit will call in 30 seconds. You have also determined that just after being supplied from the boiler it will take 3 minutes of probably just running straight hot. That by itself is at least a 6 to 1 factor .... which depends strictly on timing. In addition you have determined that the DHW aquastat has a relatively narrow 5 degree differential. The good part, is that it will do a better job of maintaining a call to the boiler when it needs more heat, the bad is it ends up being a smaller buffer and can be satisfied easier resulting in the boiler turning on and off more frequently.

Lastly ---- we are guesstimating about how your system may operate. Without seeing or watching it, many times the best we can do is guesstimate. But you are living with this system. More importantly, you have a passion and a degree of curiosity about it. I truly believe all you need is your hands and eyes. Go feel those pipes in your basement after the system has been off for a while. Which ones are warm, which ones are cool, and which ones are hot. This will tell you where your heat maybe or may not be going. Trust you hands..........they are my best temperature indicators. I guarantee you..... you will find a few surprises!!!

Good Luck Alex