Static pressure concerns

[seadragon]

Hi everyone,

Well, I have been reading a lot about the Infinity control and finally got one. I had my installer come out a couple of days ago and switch out my Thermidistat for the Infinity. My furnace is the 58MVP-060-14 170 series.

Anyway, I have observed that when on high stage heat, I have the following readings:

Blower CFM = 982
Inducer RPM = 3345
Blower RPM = 933
Static Pres = 0.56 (goes up to .060 at times)

I have the stat set for Comfort (instead of Efficiency). I am using the Carrier 4" Media filter.

My concern is that the static is too high. I know the PD sheet for the furnace states it can handle up to 1.0 in high stage, but I just need to know if I need to have this looked at.

As far as the ductwork goes. I was present in the house the day the installers were putting in the ducting. The house is just under 2 years old BTW: I remember commenting that the trunks were bigger than our previous house and the installer said that they have to install large trunks for this type of furnace. The return drop beside the furnace is 24" x 10. The return trunk is 24x8. On the supply side, the trunk coming off the furnace is 24x8 then it splits into 2 trunks, one being 18x8 and the other 10x8 which then go off to feed the registers. The register ducts vary between 4" up to 7" depending on where they are.

The problem is that the installer I have been dealing with doesn't exactly instill confidence in me that they know what they are doing. They just don't seem to be "up" on the details of HVAC. For example, I had them come to clean the orifices on my 2 gas fireplace (bought from them) and the guy just stuck a wire in the orifice and cleaned it out. I had read that you should NEVER use a wire to do that. I asked if he would pull the orifice out and clean it and he said that they never do that. They also installed my AC without a TXV (never mentioned it to me actually) and I have read here that all variable systems should have one. These are the things I am getting frustrated with this after spending over $12,000 with them for all my stuff. Anyway, that's another story. I find that I seem to know more about these things than the guys that show up here, especially after reading this forum.

I am just peeved since I spend good $$ on a high end system and now I think I have a static pressure issue.

BTW, the filter was new about a month ago and still looks clean.

Any thoughts on this would be greatly appreciated.

Thanks!
Ken (aka seadragon)

[dash]

The ESP is well within range ,for now ,the media filter is likely .2 or greater.

You need to check what is is in the cooling mode ,with a wet coil,when the weather allows.If it's thre tons or more ,it's likley to be higher then it is now.2.5 tons maybe higher also.

[seadragon]

Thanks for you reply dash...

My cooling system is a 2 ton Carrier 38TZA. I was getting a little paranoid from reading previous threads that mention 0.5 should be the max for residential systems.

[dash]

The lower the ESP,the better,if you want to get it a little lower,have them add turning vanes to the 90° turns in the return duct.


Lower ESP,will reduce the indoor fan operating cost,so there is a small payback.


With 2 tons the airflow will of course be less in cooling,so the extra static of the wet coil,with reduced cfm ,should net a lower ESP in cooling.

[garry b]

Seadragon...you have very acceptable static. My system is a bit 'noisy' (air movement noisy) but I'll see about having corrected in the near future. I'll bet if they replace the main supply and return ducts things will smooth out for me.

low fire/efficiency

air flow: 1320
rpm: 1124
static: .98

high fire/efficiency

air flow: 1460
rpm: 1207
static: 1.11

[Edited by garry b on 12-04-2004 at 01:43 PM]

[dash]

Originally posted by garry b
Seadragon...you have very acceptable static. I had a variable unit w/air retrofitted to existing duct work. My Evolution control indicates "1.06" for static, on low fire, "efficiency" operation. It's a bit 'noisy' but I'll see about having corrected in the near future.

Try to get it corrected ASAP,that's way out of line.

Any pictures of the duct system or details ?Have they tested the supply and return separately to see which is the highest?

[garry b]

Dash...I posted this way back in July c/w pictures. The work done was good but no one did any manual checks for duct sizing, etc. Only a manual was done for furnace sizing.

My tech is a friend who's always up to his butt in work. He's coming over when things levelled out and at that point I'm gonna give him the 'what for' and see about checking pressures, temp rise, etc. If he takes much longer, I might have to light a large fire under him.

[garry b]

Well, finally I got someone to measure some static on my system.

First off...I must say that my Aprilaire 2400 filter that's been in use for 17 months was due for a change. My tech pointed out that if you look on the downwind side of the filter and it appears to be black, it's finished. This will coincide with the "change your filter" flag coming up on the Evolution control. So, now we know the "change your filter" flag is pretty accurate.

Now, about the static. System running on high fire, high fan, 1465 cfm, static was measured at the blower compartment (not above the heat exchangers which I though was kind of not right) and also upstream of the filter. The blower compartment static came up at 0.55 inches. The pre-filter static came up at 0.25 inches. So, total static running balls out is 0.80 inches. Just for the record, the Evolution control is showing something like 0.93 inches. So, now one wonders which number is actually correct? The evolution or the digital gauge he used?

About taking static at the blower compartment...I thought the static should have been taken above the heat exchangers and below the a/c coil? But since he took it at the blower compartment, is it actually giving a false high reading?

Bottom line...the tech says the unit is running as it should considering the ducting, a/c coil, etc. Also, he doesn't feel that duct corrections are in order as the unit isn't running out of spec by any horrendous amount (my words). Temp rise is right on the money, too...mid-range so to speak. Gas valve was also adjusted...the high side was high and the low side was low.

FYI, we actually run this unit on the 'comfort' setting and it primarily runs on low fire and fan except when making up temps from a set-back period. Tech mentioned that the best efficiency is actually found with the lower fan speed. So, our actual static will be lower since we do run a lower fan speed.

This is fyi but if anyone has any comments, I'm all ears.

[stevies3]

How do you calculate static pressure?

[falltime]

seadragon our system is 1week new our readings are air flow 1069 blower rpm 964 static press.57 this is at high heat

[tuccillo]

My Evolution system staitc runs from 0.1 to 0.4 depending on whether it is in high speed or low speed and how many zones are calling.

Originally posted by falltime


seadragon our system is 1week new our readings are air flow 1069 blower rpm 964 static press.57 this is at high heat

[seadragon]

I just had a look at my Infinity readout now and it is running on high heat.

Readings are:

982 cfm
914 rpm
0.54 static pressure.

I have a bypass duct for a humidifier which is currently open and drops the static pressure a bit. I have seen it go as high as 0.67 in the summer when in cooling mode. I changed my media filter at the beginning of October.

[jrbenny]

Originally posted by garry b
So, now one wonders which number is actually correct? The evolution or the digital gauge he used?

I have no doubts as to which one is correct. It is quite easy to incorrectly measure the static pressure...especially on a residential system.

The Infinolution is extremely accurate.