Eliminating taco mixing blocks?

panman

I have 3600 sqft. New home. trinity ti150 gas on the wall boiler. 5 radiant zones. 2 taco mixing blocks. Mixing block temps drop from 130 to 90 if more than 2 zones are on in 10 degree weather. I do not believe my boiler is capable of keeping temp. Down stairs taco runs 24/7 in cold weather because it only circulates 90-100 degree water most of the time.I need hotter water down stairs because of pex 4'' placement in cement.  I want to eliminate the 2 taco mixing blocks and pump a straight 140-160 dgree water in what ever zones needs to be heated so it can shut off. i do understand how radiant works but am willing to put up with the heat temp swings. Furnace/taco blocks= not very effecient. What are my options? Thanks for your time. 

Zman

Outdoor reset

You certainly don't "need" the mixing blocks. I would suggest having the boiler modulate based on it's own outdoor reset curve.

The mixing blocks are not a bad product nor are they inherently inefficient. I suspect something else in your system design is the culprit. Do you have pictures? How are the blocks controlled?

Carl

panman

re- outdoor reset

Zman, I know the taco mixing blocks are not a bad idea, but where my pex down stairs is 4'' in the cement, i would rather have the furnace pump out 150 degree water to both down and up stairs and get the thermostat met. A mixing block running 24/7 when it's cold cannot be very effecient. Is my Trinity capable of pumping 150-160 degree water to 4-5 zones if i did not have mixing blocks? If i can get the zones met quicker, than it will be less times that all my zones are running at once.I do not believe my propane consumpyion would be much different. I also loose some boiler heating time when my 80 gallonAmtrol is running for hot water which does not aid the situation. Thanks

Zman

Something else...

Your mixing blocks are designed for systems like yours. There are a handful of settings that need to consider. http://www.taco-hvac.com/uploads/FileLibrary/102-151.pdf



Are you saying that the injection pump is running 100% and still won't keep up?



Is it in outdoor reset mode with an outdoor sensor?



Carl

panman

re- outdoor reset

yes the outdoor reset is set with 2 sensors. The down stairs taco mixing block runs 100% only when the temp drops 10-20 degrees, but thats when the upstairs zones might call for heat also. In short story, each taco drops temp circulation when a zone opens. If 1 upstairs zone opens while 1 downstairs zone calls for heat then the temp at the taco mixing blocks does not keep the temp it runs when just 1 zone is calling for heat. Example, on cold day 3 zones running, both taco mixing blocks are circulating water at 100-110 degrees. We both know that stapled aluminum fin should be 140-160 and because of my pex not being 2'' and being 4'' in cement i really believe i should be running at least 130-140 through pex. Should my Trinity 150 be able to keep up with that demand or down the road should i get a little bigger boiler. Thanks for your advice!!

CMadatMe

Multiple Water Temps

Your high temp radiant should be running off the boiler outdoor reset curve and the low temp radiant off the mixing block. You cannot run both the slab and staple up on the same water curve. It's a piping/design issue. A radiant mixing block will also only deliver a maximum of 12 gallons per minute. Your radiant slab should be running on a 10 degree delta-t whereas your staple up a 15 or even 20 dependent on if you used plates or no plates.



You have 2 different types of systems and trying to make them into 1 type. Not going to happen.

panman

re- outdoor reset

Thanks chris, i am just inquisitive enough to look into this because i want to understand my heating system. I do know radiant is a different animal than baseboard. I am not sold on the system that i have. Outdoor reset curve, Delta-t and taco mixing blocks, to me are a way for the electronics to tell my boiler and mixing blocks at what temp to heat my home supposidly the best temp for the best situation. Amuse me for a minute!! If i had 2 groundfos circulators(eliminate taco blocks), 1 for 2 upper zones and 2 for the downstairs zones. If i set my furnace to run 140-160 with the 20 degree differential, 1 would my trinity ti150 handle it. 2 Other than a little temp swing on the concrete zones, what are the possitive and negative. Thanks for your input and time!!

Dave H_2

Don't replace, reprogram maybe

You've got a lot going here with electronics and they are trying to make your home as comfortable as possible and also energy efficient.

You boiler is operating on a reset curve, it may need to be adjusted to get hotter water to the RMB's.

So the RMB is also modulating temperature based upon outside conditions and a target supply water temperature. If the boiler is not putting out a high enough water temp, then the RMB is starved and won't heat adequately.

The idea behind the RMB's is to modulate water temperature and to prevent major swings in air temperature. If they are removed and a very high temperature is sent to your floors, here is the scenario that take place;

Room is 69 degrees, setpoint is 70. Zone has not called for hours. Slab is cool, water in the slab is cool.

Call for heat occurs and the slab starts to heat up, you have 140 degrees slamming into the slab. Radiant is a slow and gentle beast, and it will take a while to change the air temp in the space. The first thing to heat will be the concrete, once that is warmed, then the air starts to warm up. Air temp now reaches 71 and the stats stops calling for heat. However the energy in the slab needs to go somewhere and it was slammed with a heck of alot of BTU's. The air temp in the space will only have to go up. It can reach 74-75 degrees very easily. This happens again over a long period of time say over a couple of hours.

Now the air temp starts to drop because the slab is cooling down. The air temp hits 69 and the stat calls for heat again, however the air temp continues to drop while the cold slab absorbs heat, before the air temp starts to climb again, it may be around 66 degrees. So now you are looking at easily a 9 degree temperature differential in the space.

I know there is lot here but to get to harsh and replace, it won't improve the situation.

There are a couple of things that need to be done,

1. A heat loss of the house on a room by room basis

2. Calculate the target water temperature needed for the RMB's

3. Adjust the boiler temp to be higher than the highest temp.

4. Make sure that the RMB circs are large enough to handle the load

5. Reprogram RMB if needed



I hope this helps



Dave H

panman

re- reprogram maybe

Thanks for all the info dave. I will check into all the points you made and see what i can do to adjust a few things to see if it will improve the downstairs in cold weather. Thanks again!!!