Ultra 155

Constantin

In a recent thread related to heating up a freshly-poured slab, a GB kept ramping down its output to reduce the ΔT across its HX to be 45°F or less. Presumably, these kinds of thermal gradients are not healthy for Aluminum monoblocks, and the Ultra may have the same thermal shock protection programmed into it as the GB142.

Hopefully, your 45°F ΔT is not a normal condition. Otherwise, you may have the wrong boiler or distribution system for the application...

One way you could "fix" the problem is by blending the returns with water from a storage tank. If it's sized properly, this could reduce the ΔT to the point where the boiler can remain on high-fire indefinitely. However, a better bet is to change the manifold piping to the point where the ΔT across the slab is 30°F or less. That way you can reap the benefits of the mod/con boiler to the fullest.

Sam_11

Ultra 155

I am wondering if any of you talented individuals have run into a problem (and know the fix)where the delta t for a radiant slab is 40 to 45 degrees. This is a new job where I installed an ultra 155 to handle as of present 2 zones one baseboard one radiant. The baseboard runs fine with a delta t of 15 to 20 degrees, but for the life of me I can not get the delta t for the radiant any closer than 40 degrees. I installed 4 loops 1/2" pex in 4" of concrete with a grundfos ups15-58f circulator. (recently up it to a 26-64f with not much change.

Weezbo

may i ask what lengths these loops are and how....

they were laid out? and more importantly what the heat loss of that area may be and if you thouroughly power purged the loops of all air in each loop? here is one last one...is this slab insulated from the ground water table? here is what could happen if one has not purged correctly one or more loops may not be fully able to function as an emmitter.and if the ground has a high water table and that wasnt accounted for maybe the btus are simply being carried away, if the loop lengths are excessively long the waters may be circulating buh losing heat due to the inability of the circ to achieve a flow rate able to distribute the btus in any other way, the lengths are important as it is also possible that a particular length is losing a group of heat on its journey and is trying to make up for a lack of flow in other areas(loops) (zones)that are not Balanced with flow.

have you tried turning the boiler off and reverse power purging each loop one at a time?with a little food colouring thru each loop? it will tell you when you have full flow through that loop.

i have seen loops that ran out and back on the same header ( supply or return0, nothing is really happening through a loop or two like that even if there seems to be heat heading out...

i seem to think that the return sensor isnt reading the actual return from the slab un less that is a picture without the baseboard zone on.

hot_rod

how long

has it been running? And how cold was the slab when it was fired? At first start up on a cold slab, that is not an uncommmon delta t.

If it has been running for sometime look for a flow restriction. Are all the manifold valves fully opened? Possible kinks somewhere? Are you sure about the loop lengths.

Is the pump running, actually spinning, and iso valves opened fully

hot rod

Sam_11

ultra 155

The slab is 1156 square feet. Each loop is 280 to 290 feet. The slab was insulated with insultarp. The picture with the digistat is with the baseboard off. The delta t for the baseboard averages 10-15 degrees. So the return sensor is working. If you noticed on the pictures I have no mixing or tempering valve for the radiant. I wired the baseoard to the DWH giving it priority when both call for heat. I also adjusted the fireing rate because the ultra 155 from factory puts out 123,000btu. The slab was sized for a max of 46,000btu. If you also look at the bictures I added a ball balve at the top of the primary boiler loop. If I close it I can get the delta t within 29 degrees, but I then have to shut the baseboard return because the boiler will syphon water from the baseboard thus heating that zone in reverse. The system is purged of air, and I get about a gallon and a half of water per loop.

Sam_11

Change the manifold piping? What do you mean?

Sam_11

As of present I set the boiler to put out 60,000 btu to the slab with an average heat temperature of 148 degrees. The slab does come up to temperature, but the boiler runs forever.

Sam_11

As of present I set the boiler to put out 60,000 btu to the slab with an average heat temperature of 148 degrees. The slab does come up to temperature, but the boiler runs forever.

Ed Cudney

Sam_11

If that where to be the case I should have a problwm with the delta t for the baseboard???

Constantin

If the loops are too long,

you get a large ΔT, along with high head pressures. If the loops are the right length, the ΔT will be very low once the slab is up to temperature. Since a slab can store a lot of heat, it will take a long time to come up to temperature. However, if it has been insulated well at the edges and below, it's load will decrease dramatically after the initial warming.

If the slab was not insulated well (either by local soil conditions and/or insulation), I guess the homeowner will be heating his/her exterior plantbeds around the home just as Dan describes it done in Levitton. A sure energy hog!

Tony_23

It's the load

It's just the pad being cold and sucking up all the heat it can.

I'd set the limit at 140 and let it ride, it'll come up to temp and the deltaT will narrow.

Sam_11

Even at temperature (slab at 78 degrees) delta t is 30+

Tony_23

well...

if your slab is at 78 and cycling, then you should be able to lower your limit temp and still satisfy the load. Maybe it'll modulate then. I'd lower the target temp 20 deg and see what happens. I'm sure that'll narrow the delta

You can't expect the bbd and slab to act the same, either. They are 2 VERY different types of emitters and will act quite differently.

Doesn't your design tell you what temp to run ?

If you put the slab on outdoor reset it would all be good.