Carrier Infinity airflow setting - impact on efficiency.

Old 10-01-13, 01:28 PM
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Carrier Infinity airflow setting - impact on efficiency.

Hi folks,

I searched and can't find a good explanation. I am having to delve into this after we paid certified technicians to help us determine the efficiency configuration of our furnace. I am sure there are great techs out there, it's just getting expensive sampling until we find the right one.

The system
A few years back we had the following system installed:
- Carrier 58MVP060-F-1 with infinity control unit/t-stat
- vents to outside with two white pvc pipes slopping downward to the furnace
- OAT wired into furnace control board
- Electronic Air Cleaner and air filter box with cleanable 1" air filter
- Single zone
- flexible ducts (insulated); registers on the floor, return in floor joists where old gravity floor furnace was
- installation configuration: bottom return; furnace in crawl space in horizontal right position
- house is just over 1000 sqf
- Climate: fairly temperate. heat needed in winter mostly. no need for AC or humidifier.
We don't expect or use the system to heat the house instantly and have smart recovery on (gradual change over 90 mins before schedule change). We occasionally use override to prolong a given heating period.

It's a high efficiency system (around 96%?), but we have been auditing the house for energy leaks, and we've been told that our system may not be set up for higher efficiency.

The questions
1) is airflow directly related to fan speed all else being fixed?

2) my understanding is that this system has a two-stage burner (off/low/high) and a 3-stage fan (off/low/mid/high) -- is this correct?

3) One of the settings in the infinity control system advanced setup is:
Setup -> Furnace -> Airflow
The setup manual says the following:
Selects the airflow of the furnace when heating.
• EFFICIENCY is the airflow used to meet specified ratings
• COMFORT (default) is a decreased airflow used to increase the output air temperature and provide increased comfort.

So, does the EFFICIENCY setting run the fan in high speed only (or some fixed high-airflow value)? I can conceptually understand this (higher air flow over a given hot surface will extract more heat, so more efficient), but I'd like to know what we are giving up by switching from COMFORT to EFFICIENCY mode.

Reading the above description tells me they define comfort as higher air temp at lower air flow (and therefore lower noise and turbulence/draft/dust).

4) Another setting is: Setup -> Furnace -> STAGING:
The setup manual says the following:
Controls the staging of the furnace.
• SYSTEM (default) setting will allow the Infinity Control to determine furnace staging
• FURNACE will allow the Furnace algorithm to control staging
• LOW will only run the low stage of furnace heat
• HIGH will only run the high stage of furnace heat

My understanding is that this sets what burner stage will be used, or who is in charge of deciding that mode (infinity controller/tstat, furnace, or fixed by user).

I'd rather leave it at SYSTEM to take advantage of the intelligence of the infinity control unit, but purely out of curiosity, what are the reasons for someone to change the setting to say LOW or FURNACE staging (I couldn't find much on what performance targets the furnace algorithm tries to maximize).

I suppose I can get some better answers for some of these by monitoring exhaust gas temperature under different settings but I'd like to hear from anyone who has some expertise with how these settings affect performance and efficiency.

Many thanks for any insight.

Last edited by ocean breeze; 10-01-13 at 01:49 PM.
Old 10-01-13, 02:19 PM
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1) is airflow directly related to fan speed all else being fixed?
The *blower* or *fan* is designed to produce X amount of cubic feet per minute ( cfm ) per revolution of air flow. So , the greater the revolutions per minute (rpm ) the greater the cfm.

In other words --- yes, the airflow is related to fan speed.

Now, that's the blower at the furnace. Airflow at the registers is affected by the ducting design , balance and installation quality.
Old 10-03-13, 08:17 AM
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tstat settings don't override furnace

Thanks canuk. Makes sense.

In the meantime, I looked a little more into this and realized the infinity tstat throws a model/setup error when I set it to efficiency. Is this because the dip switch SW1-4 on the furnace board is set to ON (Comfort)?

EDIT: The infinity control manual says the following:
No settings will need to be made at equipment (i.e. DIP switches on a furnace). All configuration settings made effective from this menu will override equipment configuration made by dip switches.

I was under the impression that the tstat settings would override the settings on the furnace (it seems to be the case with all the other settings), but it clearly isn't here. I'll try to set the dip switch to efficiency and see if the tstat will let me switch back and forth.

In the meantime, if anyone knows, I'd appreciate any help.

Last edited by ocean breeze; 10-03-13 at 10:18 AM.

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