Is this normal modulating/condensing behavior?

jetpeach

see the manual here
http://www.blueridgecompany.com/documents/LaarsHT330.pdf
from this page
http://www.blueridgecompany.com/radiant/hydronic/503
(the laars mascot ht330 is the same boiler/manual as the baxi luna ht330) and see the keys to press to make the adjustment yourself. you have to cycle through quite some options, but the manual explains reasonably well what they mean, though you may need to read a bit more.

Steve Goldstein_2

Is this normal modulating/condensing behavior?

I have a Baxi Luna HT modulating/condensing boiler that was installed last April. An outdoor temperature sensor is connected to the system. For zones, I have five copper fin baseboard zones, one MegaStor DHW zone, and one hydro-air zone via an air handler.

The Baxi has a display on the front of the unit that indicates the temperature of its internal water (at least that's what I think it's indicating). Once it fires and brings the zone up to temperature, it levels out at 80 degrees C (176 degrees F).

I know that the hydro-air zone requires the system to run at a temperature that's hotter than ideal for optimal condensing, but that's not what surprises me. What surprises me is that the system always levels out at 80 degrees C. I thought that, with the outdoor temp sensor, the system would change its temperature dynamically (on a day with warm outdoor temps, it would run at a lower temp than on a day with cool outdoor temps).

Is this normal behavior, or is the system not configured correctly?

Thanks,

Steve

ABD

With copper-fin and hydro-air, you probably can't use water much cooler than 80C. There is no point in having a condensing boiler with such a system.

It sounds like it is not configured correctly, but even when configured correctly, you won't be able to have temperature variation.

Unknown

What do you base that on? Hydro air and copper fin can both often be run much cooler than 80C.

Unknown

Not configured correctly.

Mike T., Swampeast MO

Does sound as though your boiler was set to operate at a fixed temperature.

IMHO, the installer has done you a disservice by not at least attempting to use reset. Hopefully the modulating feature is not locked out as well (don't know if that's possible). As is, you're gaining very little from condensation and only stand to gain from modulation.

Fin baseboard can DEFINITEY use reset and there's a decent chance it doesn't even need to be 180F at design conditions. While the reset slope is shallower than with many other emitters, it can often go surprising low in moderate weather.

Hydro-air is another concern. While it certainly can be designed for operation at significantly lower temperatures, the coil size must usually be increased. (Anther way to is to increase the flow rate, but you rapidly hit a point of little return.)

A significant problem with hydro-air and reset is that the blower speed of the hydro-air unit is generally fixed. As you lower the supply temperature, the air temp reduces as well. You can have a situation where even though it's producing enough heat, the air temp is low enough and air velocity high enough that you're uncomfortable because the system is blowing "cold" air.

Thus, a typical hydro-air unit will generally need an even flatter reset curve than fin baseboard and you MUST set the curve to satisfy the most temperature hungry portion!

Personally, I think the installer owes you a call to complete the setup--sounds to me as they left it for "guaranteed no callback for lack of heat". If you're at all technically inclinded, I suggest you ask how to adjust the reset curve of the boiler and perhaps the fan speed of the hydro-air unit.

With some careful adjustments made in small measure over a significant period of time you can likely better exploit the capabilities of your boiler.

One last thing: If you're using much (or any) daily setback in the hydro-air zone, your opportunity for energy savings from condensation diminish...

Steve Ebels_3

Au contraire

I have many BB systems running on reset that go all the way down to the low 100* mark before the boiler goes into WWSD. They work well on most system and do beautifully on systems with what would be considered "excess" tubing length.

Boilerpro_5

Right on the money, Steve

My baseboard and hydroair systems run on full reset, right down to 70F supply water at WWSD. And the majority of baseboard systems will do just fine with about 160F supply water at design day.

Boilerpro

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Patrick Linhardt, \"Linhardt's Field Guide to Ste

I concur

Hi Steve,

I also have a hydro-air system, a converted heat pump air handler. I vary the water temp to a hot water coil with a variable speed injection pump, through 1/2" PEX to boot. It is a three pump application, one at the boiler, the variable speed, then one on the coil(runs continuous). My water temp varies from 70 or so to 170. My wife has never been more comfortable.

Sorry to disappoint anyone who thinks I have a steam system. I bought the home for the school system, not the heating system.

Best regards, Pat

Bob Sweet

Steve,

what model Baxi do you have, 1.33,1.45 or 1.65?

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Steve Goldstein_2

Baxi model

I have the Luna HT 1.33.

And to Mike T, I know the modulation isn't disabled. I can hear the flame throttle back after it first fires.

Thanks,

Steve

Steve Goldstein_2

??

Pardon my ignorance, but what does WWSD stand for?

Mark Hunt

WWSD =


Warm Weather Shut Down.

The outdoor temperature at which the boiler will stop firing for heating.

Mark H

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Bob Sweet

Steve

With or without the sensor hooked up the boiler will modulate it's fire rate, either off of outdoor temps (with sensor hooked up) or return water temps (without sensor). With the sensor you have many heating curves to choose from based on the desired slope of the curve you want. IF the sensor IS hooked up which it might not be, the curve that has been selected seems pretty steep and could be adjusted within the QAA parameters. I would verify that the sensor is hooked up, and has been properly adjusted for your system needs.

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Steve Goldstein_2

The sensor is there

I can tell you that the sensor is physically installed (under my porch), and that it's wired into the Baxi. Whether the installer configured the Baxi to utilize the sensor and, if he did, whether he configured it optimally, is what I'm trying to determine.

Is the installer the only person who can adjust the QAA parameters, or does the temperature knob on the front of the Baxi affect the curve? I'm wishing I could control this thing and optimize it myself, without having to rely on the installer....