TT 170 problems recovering in high mass system

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  #81  
Old 01-16-12, 04:47 PM
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If the pumps moving more than 10 GPM through the boiler the output temps go down. Yes, the boiler might still be generating its rated BTUs but the heat transfer in the living space is going to suffer with 155 to 160 degree water in the radiators vs. 170 to 180 degree.

With this in mind, if the boiler can't produce at least 170 degree water at outdoor design temps then the boiler is too small. Is there an error in this logic?
I may not be 100% correct about this, but with the water moving slow, it will pick up the BTU's in the boiler. The problem arises in that because it is moving slow, the first radiators the water reaches will transfer more BTU's into the air before it gets to the radiators at the end. So you will have uneven heating which can affect the way the thermostat calls for heat.

You need to know your heat loss to know if your boiler is too small. The water temperature needed to satisfy your heat loss is based on how many sq ft of EDR your radiators have. The less you have, the hotter the water. The more EDR, the cooler the water.

Don't forget you are going to save money in heating by switching to natural gas. So don't focus too much on the unused unit being heated.

I don't know how things are in Portland, Me, but I have been reading a lot of articles on how apartments are in demand. A lot of new construction are new apartment units. So spending the money on that 4th unit may not be a bad idea to do sooner than later. Of course, do your own research as I am not an expert.
 
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  #82  
Old 01-16-12, 05:02 PM
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And all that assumes an efficient emitter system, etc.
Wouldn't that be a given, being it's a converted gravity system?


Peterr
 
  #83  
Old 01-16-12, 05:05 PM
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Have you contacted Triangle Tube for their advice by any chance?
 
  #84  
Old 01-16-12, 05:16 PM
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I believe the boiler won't be able to keep up if there's more than 10 GPM of flow through it.
But why wouldn't it? A 100K BTU boiler would be able to keep up with that flow with a 20 DT across the boiler. Wouldn't it?

Shouldn't you be able to flow 15 GPM through a 150K boiler with a 20 DT... right?
 
  #85  
Old 01-16-12, 05:35 PM
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Shouldn't you be able to flow 15 GPM through a 150K boiler with a 20 DT... right?
Exactly NJT.
150 degree water at 20 degree delta T, moves 154,000 btu's hr., at 15.7 GPM.

I tried to cover this nearly 80 posts back.
The TT throttles itself down to protect itself if the delta T gets over 45 or thereabouts.
Which corelates exactly to:
161,500 btu' hr, at a 42* delta T and 7.9 gallons a minute.
The spec for that unit is 8GPM minimum.

Rufus is having trouble understanding that a hotter water temperature doesn't mean more heat.
When there is less flow.

Peter
 
  #86  
Old 01-16-12, 09:23 PM
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I believe it i a common missperception that a high rate of flow thru a boiler will reduce the amount of heat it can produce.
Yes it can reduce the maximun temperature of the supply water.
However the total amount of BTU's produced and delivered will be the same.
Remember we do not heat with btu's, yeah I know simplifying this but just follow, we heat with hot water. Water temp is what is important. Let's say we need water flowing at 180f to heat the home @ 0 degrees. The boiler doe output is 100,000. If we move 10 gallons of water through the boiler we will be at a 20f delta - T. We add 20f water temp as the water passes through the boiler. Slow the water down to 5 gpm, a 40f delta T hotter water at a lower flow rate and raise the water temp by 40f as it passes through the boiler.
Both examples the boiler put in the same amount of btu's but split it up into more gallons on the 20f delta-T.
Now let's look at the system.
Move 4 gpm of 120f water from the 100k boiler we will get less heat from the radiation than the same flow of 180f water. Radiation works on water temp and flow. Same btu input but higher water temp will give off more heat in the system. With p/s you will end up with the same water temp leaving the supply tee after mix with a 20f delta-T or a 40f delta-T from boiler and blending with the return water from the system.
Again higher water temp to radiation gets more heat to the room however we need to make that happen. Slower the water goes through the boiler the hotter the water but less flow to system. Increase flow to system and increase heat output as long as the water temp is high enough to get the proper heat into the room.
I also agree that the manifold piping should be at least 1-1/4" all the way through and reduce to the separate zones.
 
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Old 01-16-12, 10:24 PM
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Move 4 gpm of 120f water from the 100k boiler we will get less heat from the radiation than the same flow of 180f water. Radiation works on water temp and flow.
There is no evidence, that this converted gravity system, with cast iron radiators (not fin tube,) is lacking in radiation and can not handle higher flows. Rather, all the evidence is to the contrary.


Peter
 
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Old 01-17-12, 09:34 AM
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is lacking in radiation and can not handle higher flows. Rather, all the evidence is to the contrary.
I have 4 weeks of history with all three pumps running at max speed. I can tell you that the apartments do not stay warm with that much flow. My tenant on the first floor was logging radiator surface temperatures with an IR thermometer for two weeks. Every 30 minutes they would log the surface temp of all the radiators in the apartment. The primary object of this data collection was balancing the system. Some radiators were hot and others were cold.

There were periods during the day where the radiator surface temps would drop 25 to 30 degrees. (no significant change in outdoor temps during this time.) These temp drops corresponded with all three zone pumps running at the same time. This prompted me to slow the pumps down using auto-dapt mode. So there's evidence that too much flow is a bad thing, IMO.

I will set all three pumps at medium speed on Thursday morning to see what happens.
 
  #89  
Old 01-17-12, 10:25 AM
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Proof positive that the radiation is not undersized.

What we don't know, is if that Honeywell control has indoor feedback used in consideration of the boiler target temperature.

I also read from this post that, zones go off and on, thus thermostats must be getting satisfied,

And also leads to questions about thermostat cycling/differntail setting, that may be far too wide.

Which leads to questions about the settings of the curve on the outdoor reset control.

Again leads to question of metering the gas comsumption on the boiler.

I think a better test might be to put the pumps on medium and set all the thermostats to 80 and then see what develops after a few days.

Peter
 
  #90  
Old 01-17-12, 01:44 PM
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Not a bad idea, although before tweaking the reset curve it would be good to get a handle on the flow rate estimates, performance (e.g., how often the stats satisfy, etc.) so there is some knowledge of the thermal flywheel for this building. Wouldn't want to change the reset curve only to find you are chasing a non-current outdoor/indoor relationship.
 
  #91  
Old 01-19-12, 03:06 PM
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So I did some more testing today. All three floors were set at 68 degrees. I waited for the thermostats to be satisfied in each zone to be sure everything was heated up and stable. Then I turned each thermostat up to 72 and manually placed the boiler in high-fire mode. I let it run for 8 minutes and started recording some numbers

The three pumps were moving 3 GPM each. The delta T through the boiler was 26 to 28 degrees at 9 GPM. (GPM was measured by the meters on the Alpha pumps.) Some quick math tells me the boiler is only putting out 117k to 126k BTUs. (9 gpm x 28 degrees x 500 = 126,000)

The DOE heating capacity of this boiler is 154,000 BTUs at 95% efficiency. The Net IBR rating is 134,000.

With this info is the boiler putting out the BTUs I should expect?
 
  #92  
Old 01-19-12, 03:17 PM
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With this info is the boiler putting out the BTUs I should expect?
That would appear to be no where close.
DOE is what it should put out. At least.

I wish you could have verified the above by reading the gas meter, before and after, say an hour's firing time.

Where do the temperature readings come from?
The boiler control panel?


You really need to meter the gas to be sure.

Otherwise, it sounds like you have found your problem.
Unless there is something that prevents it from putting out 100% that you can not override?

Peter
 
  #93  
Old 01-21-12, 06:30 PM
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Still trying to figure out why we're not getting full fire out of the boiler. The rep is recommending we check the fan speed and also see if the intake and exhaust runs are within guidelines.

I opened the boiler cover today and noticed that the manufacturing date on the heat exchanger is 2008. I was a little surprised. Would it be normal to have a 2008 heat exchanger in a "new" TT170 unit installed in November of 2010?
 
  #94  
Old 01-21-12, 08:34 PM
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Quite possibly. Particularly given the state of the economy since then.

You really need to meter the gas. Boiler could be starved for fuel.
 
  #95  
Old 01-22-12, 11:54 AM
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Their service tech came by and did a combustion test on Friday and left. I was told that everything is fine with the boiler as far as they can tell but they are planning to look into the possibility of the piping runs being too long and not allowing the proper airflow through the boiler.
 
  #96  
Old 01-22-12, 12:19 PM
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A combustion test... ok... but did they check the gas pressure?
 
  #97  
Old 01-22-12, 02:05 PM
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What size is the manifold piping? It should be 1-1/4". Pictures are deceiving but it looks like 1" pipe. If so the pipe size can affect flow through the boiler and heat output.
 
  #98  
Old 01-22-12, 06:26 PM
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Yeah, that pipe size has been mentioned and ignored a few times in this thread...
 
  #99  
Old 02-17-13, 12:43 PM
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Just an update a year later

The manifold piping is 1 1/4".

The system has been converted to a P/S setup with a Taco BumbleBee set at 30 degree delta T as the boiler pump. It runs awesome now.

The root cause of the "problem" is a safety feature built into the TT170. It will raise the water temp by 40 degrees above the return temp. So if the return water is 80 degrees the boiler would only raise the temp to 120. The house heated well with each zone direct piped to the boiler (no P/S) if (and only if) all three zones were heated to at least 65 degrees. If one floor/zone was unoccupied and the thermostat was setback to 50 the return water temps from that zone were low enough to put the boiler into it's safety mode.

Now with the P/S setup deep setbacks are not an issue. The Bumblebee automatically speeds up or slows down to maintain enough flow through the boiler for the proper delta t. Now we don't have to pay to heat vacant space in order to keep the occupied spaces comfortable. Our utility bills have dropped by roughly 30%.
 
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