Garage infloor and Air handlers

sheat

I have a 3 zone hydronic system Mudulating/Condensing boiler doing 2 hydronic air handlers and a zone of garage infloor. The air handlers need 180 deg water temp to work properly and anything less just makes them run alot alot longer. Each zone is zoned by pumps into a relay panel. Also have a indirect tank wired to the boiler for priority. The problem i have is when the garage zone calls for heat the return water from the garage loop is so cold coming back (like going out at 120 deg f coming back at 65) that it returns back into the boiler, the boiler cannot then deliver the 180 to the air handlers. ( I cant seem to get that delta t down. Its a 5 loop system, no glycol, 300' loops and say 120' of 3/4" pex feeding the manifold. This loop has a Taco 007 on it which is pretty much right at its max of the perforamce curve.) I keep the garage air temp at 60 deg f.
I do have one of the air handlers prioritized to the relay control but that doesnt help me when the other air air handler calls. I wish i had a way to keep that infloor garage loop from coming on while both air handlers are running. The boiler is for the most part undersized as it was sized only for the original house and there has been some additions. My fear is that even if i upsize the boiler to maybe what it should be around 110mbh (right now is 80mbh) will i have the same problem in the way of the boiler not being able to send out 180 deg f water to the air handlers.

Any thoughts or ideas would be great,

bmwpowere36m3

Does the return temp ever come up? Maybe you need a larger circulator for the floor radiant. Heat loss?

sheat

i keep the garage at 60. Thinking that is a fair temp. The circ is a Taco 007. I have 5 loops of 1/2" pex 300' a piece plus 120' of 3/4" pex total for a run out to the manifold. ALso in the line is a 3/4" mixing valve with a 3' pressure drop. All in all it adds up to basically the Taco 007 being at its limit/high end of the curve, but i just am not 100% sure if i change out this pump if i will ever get a 10 degree or 10 degree delta 10 on this loop. No glycol in line just water.

JeffM

Sounds like your garage is thermostatically controlled, which may not be best for your situation as the slab starts each cycle cold and takes ages to get up to temp. Have you thought about running the slab circulator constantly, and then either putting that water temp on a reset curve or perhaps using powerheads on the manifold to shut 3 of the 5 circuits via the thermostat?

sheat

I don't really want to run a pump continuously. In summary my major issue is keeping that zone of garage infloor off when 1 of the 2 air handlers calls for heat. It's almost like I need a taco relay control panel with 2 priorities, 1 for each air hAndler but can't find such thing. I'm sure there is a way to wire it up through some sort of relay I'm just not a electrical guru and neither are most electricians in my area! They can wire a plug but when it comes to relays and controls stunned.

Harvey Ramer

Your garage floor probably doesn't need 120 degree water. Turn the water temp down till you reach the point where it can't keep up or the airhandler problem goes away. I would start with 100 degree water and go from there.

What you really should do is calculate all the heat loads and see exactly what everything needs. That would include CFM and air Temps on the airhandlers.

Snowmelt

Yea I'm kinda used to 140 degrees on a wet air handler, you may want to look at your fan speed.

Zman

I think the best plan would be to install a smart mixing valve like a Taco I valve. With that installed you can not only set it up for outdoor reset so you will not overheat the garage, but you can also install it a boiler protection sensor that will automatically change the mix temp if the boiler temp is reduced below the desired level.
A pretty simple fix...

Carl

bmwpowere36m3

You really should figure out your heat loss first.

Then decide whether you want the system to respond quickly and run for short periods of time… or run for longer periods at a more consistent temp.

The first will require more BTUs and likely more GPM. The second will require less, but will need to run for longer periods of time… ideally on the coldest day constantly (all day long).

With a big concrete slab you want to run constant circulation… if too much time goes by between calls for heat its going to cool off. When it cools off too much and the GPM is too low, the water will return cold (from the loop).

There are boilers and controllers that allow for priority, multiple water temps, ODR, etc…

Zman

I did miss the part about the modulating boiler.
What model is it?
If it has limited control options, you would maximize efficiency and correct you problem with a tekmar configuration that would handle all this smoothly.

hot_rod

A cold concrete slab has a huge appetite for BTUs, it has the potential to keep the boiler temperatures low for extended periods, unless you introduce control logic to lower it's appetite. That will of course slow the ramping up of the slab.

The math involved would be the mass of the concrete and the fluid, divided by the energy required to raise it. A yard of concrete, about a 10X10, area is around 4000lbs. Calculate the area of the slab to get an idea of how much thermal mass you are trying to warm. It's a huge load even starting at 60° slab temperature.

The mass of that slab drives the thermal equilibrium (operating condition) of the boiler.

Gordy

Some details.

Is the garage floor insulated?
Is the garage temp maintained at a constant 60?
What outdoor temps does this problem rear its head, or is it consistently over an OAT range?
Are you using ODR?
What are the floor temps in the barage...I mean garage.
What is the tube spacing?

Using a slab sensor in the garage area will give better results. An air sensing thermostat in a garage can give wild control depending on its location. Say on a shared wall with the house, or on the wall by the garage door, or a window. Maybe that window gets sun.

edit : is there flow gauges on the manifold for the circuits?

Roy_2

Everyone has the right idea - heat loads first then balance the flow in the system. With 120° water to the slab you are probably getting some big swings in temp in the slab - Not ideal - and will cause a problem everytime the garage calls because it has cooled down farther then it should. A cold slab will suck btu's for a long time and with a marginal boiler your load is too great. A slab sensing thermostat will help and will maintain the slab close to the temp it needs - so no large volume coming back trying to bring it up. Still it will probably never work right your boiler sounds too small.

To do what you want a simple Normally Closed relay installed on the wire from the thermostat in the garage to the relay ( low voltage solution) or installed on the wire to the circulator (120 v ) solution. Activate the relay from the thermostat wires on the air handlers ( use isolation relays since your electrical mechanics seem relay challanged) you can also use the 120V wires to the circs to pull open the relay. RIB relay can do this.

This will energize the relay when either of the air handlers calls and open the circuit to the pump on the radiant loops shutting it off.

My suggestion - do it right once rather then playing with it forever.
Roy

Zman

@roy,
I am not sure how you are concluding that boiler is too small with the info provided.
The underlying problem is the appetite of a high mass slab.
A proper heat loss should be performed to evaluate the sizing of the boiler and the appropriate water temps for both systems.
The bang, bang relay approach you are suggesting will assure the fan coils get enough heat, it does nothing to properly manage the garage slab.
Any high mass slab should have ODR controls at the very minimum.
Carl

Harvey Ramer

I suggested turning down the temp to the garage because it is the easiest thing to do and costs nothing. Since it is a garage and it's kept at 60 degrees, I kind of deduced that exacting temp control is likely not a very high priority.

A slab can eat BTU's like mad. Turning down supply temp normally decreases BTU input significantly.

I am the first to agree that ODR is a needed component for slab control when trying to achieve a setpoint temp and eliminate swings. In this case however, a garage kept at 60.... I would turn the supply temp down if possible and not fuss to much with components and controls.

IMO

wrxz24

For what it is worth, I have the same problem. My first floor house and garage is radiant slab. My second floor is bb. During cold snaps, the boiler struggles to make high temp water because the slab, particularly after a sunny day, gobbles up the btu's after the water in the slab cools. To remedy this, I put in a slab sensor but am still trying to figure out what to put the minimum setting to.
I also have throttled down the radiant zones and that seems to help.

sheat

Thea garage is 1500 sq feet with 11' ceiling. 1- 14' x 8' garage door and 1- 8' x 7' garage door and 1- 3 x 7 man door. Insulated to r20 in the walls and the heated slab is insulated with r10. I was running 120 deg f water to the garage slab only by default as I figured it would only satisfy the thermostat faster. I am not sure how lowering my supply water temp is going to boost my return water temp? Proper manifold on the 5 loops showing .5 flow in each loop. I don't have Odr running on the boiler or any of the loops. OutdOor design temp is 3 deg f. Boiler is a weIl McLain ultra 80 condensing modulating. Forgot to mention the area over the garage is a 900 sq foot inlaw suite where one of the air handlers does it's thing. The balance of the sq footage between the inlaw space and the garage is insulated ceiling with r31. Garage is constantly kept at 60 deg. Air temp. The tekmar 509 stat is located on a interior wall with no effects hampering its performance. The garage slab is approx 5" thick with watts oxygen pex on 12" centres. So to recap the main system info. I have a boiler feeding 3 zones with a taco relay panel all with pumps. 2 air handlers, 1 for the main house which is approx 2200 sq ft, the inlaw suite which is approx 900 sq ft and the garage slab which is 1500 sq ft. Doing the math I get it the boiler probably comes up a little short, however I am afraid that even if I upsize to say a "proper boiler" in the 110mbh range I will still have the sane problem when the infloor in the garage comes on along with one of the air handlers. Comments are good. Thanks Roy for the relay comment that's what I am looking for. Maybe you have a specific part number you can suggest?

wrxz24

What was told to me was that lowering supply temps, more of the btu's would be available for the high temp. Less of the hot would go to the garage if you kept the temp lower than 120. Once the garage floor is stabalized, less return water back to boiler as most would go back to floor with only a little supply to floor. That is why constant circulation is a good thing if you can match heat loss with outside temps.

Zman

Lowering the mix temp will correct the problem. It will lower the temp differential between the slab and the water and less btu's will be transferred to the slab. You should try it. It will cost you nothing.
The relay switch will fix the problem of cold fan coils but will do nothing for your overheated slabs.
The problem you are not seeing is that you have a high efficiency boiler that is not condensing, therefor,running like a low efficiency boiler.
I would spend a few bucks and put a tekmar controller on it.
Carl

Rich_49

Why do you believe you need 180 to the air handlers ? The problem as you are saying is that with lower water temps they run too long as I understand . If they are not running long neither is the boiler which really needs to run longer cycles with lower return temps . In other words , your 90+% equipment is probably running at around 87% . The better idea would be to make sure the airflow is balanced and fine tune it so the boiler and air handler run longer . many hvac contractors think they should be moving too much air , they size the ducts too small and use too much velocity actually making the occupants feel air movement and decreasing system efficiencies . The only thing that will determine water temp to a coil is the duct design and coil selection , this is rarely done correctly . We set up AHUs we pipe to to run at around 150* with a 20* Delta T and go down from there using ODR . A house is always the same volume so varying fan speed makes no sense . Will the house ever change size ? No , but it will require the addition of different temps at different loads . ODR on the AHUs is the key but rarely , if ever , will you need water above 145 - 150* through that coil .
Who installed the slab tubing , do the supplies enter the slab on the outside walls and cool to the interior ? A reversal here can also make a properly sized pump and the control strategy used act funky . Slab may never get where it should be and is calling too often . Was the head required for the 3/4' factored in ? You should probably be seeing no more than a 20* Delta T in the overall circuit . Plain and simple if the right sized pump is not performing the way it was designed there are 2 choices , something is wrong or it was not designed properly . You need to identify what the problem is and eliminate them one at a time to determine what to do next .
Start by eliminating potential problems to get to the correct answer .

Gordy

Your AWT to the garage is 92.5 right now 120-65/2+65=92.5

At 2.5 gpm to the garage. 5 loops .5 gpm =2.5 gpm your dumping 68750 btus in that slab 1500 SF that's 45 btus a SF.

Something is a miss here. Those garage door areas must be gobbling serious btus. No mention of perimeter insulation above.

SWEI

One of the better strategies we have found for intermittently occupied spaces like this is to maintain the space at a low but even temp (typically 50-60°F) using ODR on the slab loop and then fire the air handler when the space is actually occupied.

Rich_49

Heat going sideways . No thermal breaks you think Gordy ? Sheat , how long are the 3/4" supply and return pipes to this manifold and are there any other devices in the circuit like flow controls , valves , IFCs that could raise the head that may not have been considered ? How do these run to the garage and is the garage detached ? Kurt , I think the radiant slab is the sole source for the garage .

Gordy

Op did mention 120' of 3/4, but not sure if that was there, and back or just there. His flow gauges confirm .5 gpm each loop.

If the loops start at perimeter, and work inward that explains some wide deltas. Btus jumping off the train like made at the perimeter. Work loops inward out at least the rwt drops by the time it gets to the perimeter, and the btus don't want to jump off as fast.

Gordy

Just sayin either we got gigo, or that boiler output is all used up just managing the garage.

Zman

Gordy said:

Your AWT to the garage is 95 right now 120-65/2+65=95

At 2.5 gpm to the garage. 5 loops .5 gpm =2.5 gpm your dumping 68750 btus in that slab 1500 SF that's 45 btus a SF.

Something is a miss here. Those garage door areas must be gobbling serious btus. No mention of perimeter insulation above.

This is my point. The garage obviously does not have that high a heat loss. It is being overheated by high temp water thus turning the slab into a 80,000 pound thermal flywheel . The OP is under the misconception that running short hot cycles to the slab is good. Lowering the temp to the slab will help. i don't think the delta would be that high if not for the cold starts.

Rich makes excellent points on the air side of this system.

Gordy

I know Carl. Getting reliable data to make some educated decisions is trouble some.

I would like to know where the 65 return is measured. Assume at the 3/4 s/r. Wonder what loop deltas are? Then there is the accuracy of measuring those temps. Some people fly around with the trusty IR thermometer shooting surfaces that will make it lie to no tomorrow. GIGO

sheat

The 65 return is measured at the manifold in the garage. The 120' of the 3/4" per is the total run out there and back. The garage is attached. There is slab insulation but no perimeter. The loop patterns are from outside to inside. There is a taco 3/4" thermostatic 500 series mixing valve for the garage loop. As for the air handlers I get the whole condensing thing but I am just having a hard time hearing the air handler run for hours at 140 deg f water and take so long to satisfy where if they run at 180 deg f water they satisfy the load quit quicker. Not bang bang on an off but much quicker than at the 140.

Gordy

sheat said:

The 65 return is measured at the manifold in the garage. The 120' of the 3/4" per is the total run out there and back. The garage is attached. There is slab insulation but no perimeter. The loop patterns are from outside to inside. There is a taco 3/4" thermostatic 500 series mixing valve for the garage loop. As for the air handlers I get the whole condensing thing but I am just having a hard time hearing the air handler run for hours at 140 deg f water and take so long to satisfy where if they run at 180 deg f water they satisfy the load quit quicker. Not bang bang on an off but much quicker than at the 140.

That explains a lot!
got some individual loop deltas?

Was spacing tightened up at garage doors?

As suggested drop supply to 100, or even 95 see what deltas turn out to be. Also reverse flow on perimeter loops. Hard to say unless some lay out is available.

I would rather run longer air handler cycles than hotter shorter cycles. ECM variable speed blowers?

Rich_49

Does anybody understand that we design for hours . Although there is a CFM measurement per room that does not discount the fact that the CFM x 60 still exists . Sheat , most coils will be equipped with an aquastat that is off @ 140* - on @ 120* or 110 -130 possibly .

Zman

@sheat.
What everyone is trying to tell you is that heating a space is not a race. With a modulating boiler, you are most efficient running at the minimum modulation with the lowest possible return temp.
If the boiler is purring along producing 15,000 BTU/hrs all day long, that is perfect. Trying to make it run at full output for short periods of time makes the system less efficient and less comfortable.
Carl

Harvey Ramer

"heating a space is not a race"

I like it! Somebody finish the poem

Gordy

Low and slow like ribs

Rich_49

Not 25 minutes like bakin a biscuit , hours and hours like smokin a brisket . Don't forget your bibs . Enough of that , I'm Fu%$^&n hungry now .

Roy_2

Zman said:

@sheat.
What everyone is trying to tell you is that heating a space is not a race. With a modulating boiler, you are most efficient running at the minimum modulation with the lowest possible return temp.
If the boiler is purring along producing 15,000 BTU/hrs all day long, that is perfect. Trying to make it run at full output for short periods of time makes the system less efficient and less comfortable.
Carl

I like it! It is not a race..As the guys have said low and slow...
The thermal mass of your garage slab will suck btu's - pretty much everything you put into it for as long as you want. The floor might get a little hot before the thermostat satisfies but with the perimeter uninsulated a lot of those btu's will grow flowers outside the wall for you. Somehow get some insulation around the outer edge.

The idea is to get the slab to a temperature which will maintain your comfort level and not exceed it. As Carl said - do yourself a favor get an ODR control for the slab and try to run it as close to constant circulation as possible. Then do the same thing for fan coils. Set the lower limit for as low as you can go and still have warm comfortable air coming out of your ducts. I usually find this at 110° to 120° but it really depends on the fan and duct work. It can be quite a bit lower if your fans can be set to run low speed - it will be quieter too. Then set the high end of the curve to 180° at your design temp - there are more settings you can play with but doing that will save tremendous amounts of energy. I always use the example of me and my 16 yo son driving on the highway. I set the cruise and the car runs smooth with just enough gas to hold it steady at speed. My son likes to be Mario Andretti - full throttle - hard braking. Who do you think gets the best gas mileage? My truck or his rice burner?

The boiler will modulate to satisfy the load - right now it is running full fire and temperature trying to bring the large mass of the garage up - get that flywheel of the garage spinning it will take a lot less to keep it moving then trying to "drag race "it temperature.
See how low you can set the garage for now try to get so it runs constant then look at your return temps. 20° ∆ T at your 2.5 gpm will be about a 25,000 btu load.

gennady

You need to stop using modulating boiler as a standard boiler. Modulating boiler on outdoor reset cannot be zoned as usual. Zoning must be done with motorized modulating valves controlled by outdoor reset controller. High temperature loop is a first from the boiler and then medium temperature loop and the last one is low temperature loop, each one using return of previous zone as inlet. This must be constant flow system, with no thermostats installed. This strategy will give you what you want.

sheat

So can a outdoor reset control be set up to run 3 or more zones all at different water temperatures. The system is zoned with pumps and at this point I would like to keep them and not take them out to switch to modulating valves. I am familiar with the tekmar make if anyone has a controller to suggest.

Zman

You could run them at all different temps. It sounds like you just need one for slabs and one for the fan coils.

With Tekmar you would use a boiler controller like the 422 and a zone controller like the 335. You would also need a motorized mixing controller and t-stats. There some other options within tekmar.

If you have a newer WM 80 with "U control" some of this could be done with the on board controller. You would still need a smart valve like the Taco "I series"

Carl

sheat

what about when the infloor is the only thing calling as both air handlers are satisfied, will this control tell the boiler only to make the temperature of water required for the infloor?- like 100 deg f or so. As the boiler has already been programmed for its hottest water for the air handlers. So as it sits now the boiler is making hotter water than required for the floor because i guess thats all it knows from what i programmed to the boiler to do. The Ultra boiler is approx 8 years old.

Zman

As long as your boiler is capable of receiving a variable external control signal (usually 0-10 VDC) the tekmar can do just that.
I think an 8y/o WM can do that but you should double check the manual.

Tap2

To answer your question about cutting out the garage while the ahu's call is simply done with one or two low voltage relays.

This would just be a temp fix for the real problem. You should have a professional come out and calc. The system.