Questions on new zoned Trane XV95

[beenthere]

That info is in the Trane manual.

[beenthere]

It is a Honeywell HZ311 TrueZONE.

Sorry, I was asking Baldie what panel he has at their shop.

[Sammer VII]

dbeach, what Beenthere is saying about the return ducts is this: Your system was setup requiring a certain amount of air flow to go across the Heat exchanger/coil. This certain amount is from all the returns you have combined. So if you were to restrict the airflow by closing a damper in the return for the "in-laws" you would create problems in your Furnace/AC system. That is why is still pulls air in through the return grills as to not hinder the air flow.

[key1cc]

Is there a number I can call at Trane to obtain their fan curves (CFM vs RPM vs pressure)?

If you don't have the installation manual let me know, I believe I have a pdf version around that I could dig out and post.
Key1

[dbeach]

dbeach, what Beenthere is saying about the return ducts is this: Your system was setup requiring a certain amount of air flow to go across the Heat exchanger/coil. This certain amount is from all the returns you have combined. So if you were to restrict the airflow by closing a damper in the return for the "in-laws" you would create problems in your Furnace/AC system. That is why is still pulls air in through the return grills as to not hinder the air flow.

I understand the need to maintain a certain air flow over the heat exchanger. Humor me and take a look at the attached cartoon. It shows two independent, isolated living spaces. One is the suite, the other is the rest of the house. Assume the two spaces have perfectly sealed construction with zero air leaks and the door to the suite is closed.

Missing from the drawing is the bypass damper bewteen supply and return at the furnace.

I've labeled four pressures on the chart. P1, P2, P3, and P4. P1 is the static pressure at the return plenum and the lowest pressure of the bunch. P2 is pressure at the junction of the suite and house return lines. P3 and P4 are the pressures inside the suite and house, respectively.

In the cartoon, the inlaw suite is heated and the house heating zone is closed. Since there are no leaks, there will be zero airfow through the house return and the house pressure (P3) will drop to the same pressure as P2. The furnace bypass damper will open by some amount to maintain adequate airflow over the heat exchanger.

As far as the furnace is concerned, this is no different than closing a damper in the return line. Now we know houses aren't perfectly sealed, so in reality some amount of air will enter the house through leaks and flow to the furnace via the return and the same amount will leak out somewhere else. I don't buy into statements that this behavior (having a return pull outside air in) is necessary for the furnace to be happy. That's the job of the bypass damper, right?

If the in-law suite supply and returns are balanced, the room pressure (P4) will be unchanged. That's a good thing because if the pressure is differnt form the outside we will either force heated air out or pull cold air in through leaks.

[dbeach]

If you don't have the installation manual let me know, I believe I have a pdf version around that I could dig out and post.
Key1

I have the what the insatller left, but did not see any fan curves in it. I'll give it a closer look tonight.

[key1cc]

I've labeled four pressures on the chart. P1, P2, P3, and P4. P1 is the static pressure at the return plenum and the lowest pressure of the bunch. P2 is pressure at the junction of the suite and house return lines. P3 and P4 are the pressures inside the suite and house, respectively.

What are the actual static pressure values? And the total external static pressure?
Key1

[dbeach]

What are the actual static pressure values? And the total external static pressure?
Key1

I did not measure the pressures. Didn't think they were necessary to discuss the basic principal at hand. Or are you driving at something else? I don't have an incline manometer, but could jerry rig something if really necessary.

[key1cc]

I have the what the insatller left, but did not see any fan curves in it....

Attached is th pdf file for the XV95.

It contains the data for each size unit along with the tables that nicely relate static pressure, temp rise, wattage draw, and airflow. It turned out to be quite a valuable document for me when I was optimizing my system. All four of those parameters (static pressure, temp rise, wattage draw, and airflow) can be measured with the proper tools. The good news is that you do not need to measure all four thanks to the tables. For me, I find it very easy and reliable to check a combination of either the static pressure, temp rise, or wattage draw....and then use the tables to infer airflow. Also I personally believe that airflow would be the least accurate measurement out of the four because I cannot account for duct leaks that may be occuring in unaccessable places (behind drywall and under hardwood floors, etc).

Key1

Key1

[dbeach]

Thanks Key1.

I agree with you regarding measurements. My experience isn't in residential HVAC, but low speed flow is what it is.

My contractor will be out today to move zone dampers to put everything on the right zone. Will check tonight to see if they corrected the unsealed attic ductwork and get this over with.

[BaldLoonie]

Sorry, I was asking Baldie what panel he has at their shop.

Zonex 4+2