munchkin 140

bobbyg_9

was your thermostat satisfied during that time of 140 F water? or did it run all of the time without stopping until it got warmer?

coalminer

munchkin 140

I recently (Dec. 20) had a Munchkin 140 with vision 1 installed my 1929, 2300 sq. ft. masonry home which was
originally a gravity hot water system, (4 inch mains). The Munchkin replaced a Burnham 299,000 btu input boiler (1983 vintage). Slant fin heat loss was 129,500 btu. I have noticed that on the coldest days that we have had in Southwestern Pa. ,approx. 3 degrees f, that the supply water temperature has never gone above 142 degrees. Would it be to my advantage to lower the supply water setting on the boiler from the factory preset of 180 and if so, why? I'm trying to understand the theory behind the mod com system.

coalminer

The thermostat was satisfied. The boiler is condensing well.

John Ketterman

You have an excess of "radiation" (radiator capacity). This is a good thing.

Here's the chain of events. Boiler puts heat into the water, water goes to radiator, radiator takes the heat out of the water. Because you have a boiler with lower BTU, but you still have radiators with the same high output, the radiators are sending back relatively cool water and the boiler doesn't have the BTU to get the water back above 142F. (Your old boiler did have the BTU to get the water really hot.)

If you look at the difference between your supply temperature and return temperature, once the supply temperature has stabilized at 142F, you will see that the difference is about 20F. Your boiler is running flat out.

Now none of this is a problem. You are doing fine and condensing and saving money.

Currently if the curve is set with an upper limit of 180F, then even in warmer weather the water heats only to 142F. If you move the curve down, then in less-cold weather the water will be cooler than 142F, and it will condense a little better and save a little more money.

On the other hand if you don't have the Vision system and so no outdoor reset (i.e. no curve specifying variable water temperature depending on weather), then resetting the upper limit to any place between 142 and 180 will do absolutely nothing. You will still always hit an upper limit of 142 determined by your boiler size and radiation capacity.

You don't absolutely need outdoor reset if 142 is the highest your system will go; your return temperature is 122 or below so you're condensing anyway. But outdoor reset will improve comfort by providing gentler heat in less-cold weather, and it will allow your modulating boiler to modulate.

bobbyg_9

What is supposed to happen is this:

program the boiler setpoint (using outdoor sensor you would program 4 parameters. (2) outdoor temps. - (function 10)warmest outdoor temp you want the boiler to come on and (function 8) the design temp. for your area. (2) water temps. - what temp. do you want when it is the (function 11)warmest outside - what temp do you want when it is (function 9)design temp.

After programming, 1. the thermostat calls for heat. 2. boiler and circulator comes on. 3. munchkin boiler comes on at approx. 56,000 btu (for a 140M) it will continue to increase its firing rate and at 5 minutes it will be firing approx. 119,000 btu. At 6-minutes in, it should go to the setpoint programmed in (meaning if it is programmed at 180 deg at 3 deg outside temp) it will fire to its maximum capacity to reach that setpoint.

If you are seeing 140 deg water at 3 deg outside, it should be because it is programmed to do that. Or, the outdoor sensor isn't sending a true temp. to the boiler (you can look at this via the status menu - check to see that it is sensing the "true" outdoor temp.)

If you could tell us the functions 8,9,10,11 I can tell you what the setpoint should be at 3 deg. outside.

coalminer

Since I have the vision 1 system I could probably move the supply set point to 150 degrees. How does this affect burner modulation? Is the boiler constantly striving to get to 150 degrees as soon as the thermostat calls for heat? I do not heat DHW with this system.

John Ketterman

Yes, the boiler will run flat out in cold weather trying and failing to reach the setpoint, which is fine. You need the boiler to run flat out in the coldest weather. If you find that the boiler is being turned off by the thermostat quite often even in the coldest weather, then it is oversized, so you can set the curve even lower than 142, and then the boiler will modulate.

In warmer weather, when the target temperature is (say) 110 or 120 or 130, the boiler will definitely modulate.

So it's not just a question of the upper limit. The entire curve needs to be set correctly for the house, to get optimum conditions for the boiler to modulate.

If you aren't entirely sure of what a reset curve is and how it is properly set, I will not try to explain it here, but Google should be able to help you. (If you do understand it, my apologies.)

coalminer

I'd like to thank everyone for their input on behalf of my mod con education. I've tried to access the vision 1 settings according to the manual and I only get the high limit and temperature differential menu. Is it possible to have an outdoor sensor without the vision 1?

John Ketterman

If you have an outdoor sensor, you presumably have Vision I. There is a separate Vision manual that tells you how to get to other menus. (The manual tells you how to enter the access code, but doesn't tell you what the code is. It used to to be 925 but I don't know what it is in newer models.)

Since you paid for Vision I, you paid for the manual, so your installer should give it to you.

John Ketterman

here's the Vision I manual

http://www.htproducts.com/literature/lp-102.pdf