Other then complying with SWS 6.6201.3a (No room will exceed +/- 3 pascals with reference to the outside with all interior doors closed and ventilation systems running) is anyone measuring room pressures, and if so, are you measuring the pressure in the room WRT the main body or to the outside?  With all interior doors closed or closing one door at a time?

Tags: air, flow, infiltration, pressures, room

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Main house and one bedroom at a time - HVAC fan only not on heat or cool

Sean wrote: > HVAC fan only not on heat or cool

Hi Sean, do you know if that protocol is specified anywhere? With many (most) newer systems, in fan-only mode,  the blower operates at a significantly lower speed than in heat or cool mode. Sorta defeats the purpose of the test. The logical test protocol for room pressure diagnostics would be to set the blower to the operational mode with the highest speed (typically cooling), no?

My initial means of testing was what ever season it was turn the temp up or down & run the test but I was told for ENERGY STAR to do fan only which made some sense as you have variable speeds & even for single speeds I think most units come shipped at medium fan & have seen techs go even lower (or for units at high change to medium) - never knew manufacturers would ramp down fan speed for fan only... The nice thing about fan only - you don't have to worry when QA is done if you were on heat & they tested in cool

As for ES - footnote 34 reads: "Item 6.2 does not apply to ventilation or exhaust ducts. For an HVAC system with a multi-speed fan, the highest design fan speed shall be used when verifying this requirement. As an alternative to the 3 Pa limit, a Rater-measured pressure differential ≤ 5 Pa is permitted to be used for bedrooms with a design airflow ≥ 150 CFM. The Rater-measured pressure shall be rounded to the nearest whole number to assess compliance."

Sean wrote: > never knew manufacturers would ramp down fan speed for fan only

Two ways this happens: In fan-only mode (i.e., continuous fan), variable speed blowers typically operate at 50% of the selected speed setting. For multi-tap blower motors (PSC and non-variable ECM), the green wire from the 'stat (independent fan control) is typically connected to the lowest speed tap. Complicating this is a fundamental difference in how the fan is controlled with furnaces versus air handlers. 

> I think most units come shipped at medium fan & have seen techs go even lower

If the installer is following a proper design spec, the default factory setting is irrelevant. Every specification I prepare calls out the blower setting, which I base on the blower performance table for the specific model I'm using versus my design CFM and external static. Depending on how the numbers fall, I may end up specifying a larger blower set to a lower setting (preferable) than the most common match-up.

But your point about QA consistency is valid, especially with source equipment that has more than one stage. For zonal pressure diagnostics and compliance testing, the system must be forced to operate at the highest operating speed, typically 'high cool'.  HERS raters are unlikely to know how to do this for the wide range of equipment one encounters.

As an aside, I wasn't aware of the 5 Pascal exception. I suppose that makes sense since the difference between 3PA vs 5PA would likely be relatively smaller at higher flow rates. But I'd like to see test results demonstrating this.

Yes...this test should be done at the highest fan speed (without messing with the installer's speed tap settings) with all bedroom doors closed. With air handlers that have different speed settings for heat vs. cool, you should choose the higher airflow, if known... and if possible to run the system in that configuration during that time of year.

The 5Pa exception is relatively new (version 8, I think) and I haven't seen any data to back it up. I suspect it was based on a complaint from a high volume builder/s who have large airflows to master suites.

We test bedroom pressure difference to the hallway all the time...mostly on systems that we design and balance. Some of our data can be seen in this Energy Vanguard article: https://www.energyvanguard.com/blog/can-door-undercuts-work-as-retu...  The worst bedroom in that dataset was at 3.9Pa with respect to the hall. Airflow with door open was 129cfm, airflow with doors closed was 123cfm...a 5% drop. Personally, I wouldn't want any more than a 5% drop in airflow with a door closed, so it seems to me that the 3Pa limit is a good one. 

ES 3.0  Rev 9 Footnote 34

  1. Item 6.2 does not apply to ventilation or exhaust ducts. For an HVAC system with a multi-speed fan, the highest design fan speed shall be used when verifying this requirement. When verifying this requirement, doors separating bedrooms from the main body of the house (e.g., a door between a bedroom and a hallway) shall be closed and doors to rooms that can only be entered from the bedroom (e.g., a closet, a bathroom) shall be open. As an alternative to the ± 3 Pa limit, a Rater-measured pressure differential ≥ -5 Pa and ≤ +5 Pa is permitted to be used for bedrooms with a design airflow ≥ 150 CFM. The Rater-measured pressure shall be rounded to the nearest whole number to assess compliance

I do room testing for the Green Build program: fan only, one room at a time (other doors open), measured WRT the hallway.

Most of the issues I find are with returns not properly panned, or not cut out (drywalled over) or sometimes debris blocking the bottom of the cavity.

OMG Mark -- Panned joists -- guaranteed duct leakage.

Leakage, yes, but to where? The interior? These are only run in interior walls (exteriors have to be ducted) and, generally they work just fine unless they have the installation problems I mentioned above. Plus, the contractors are much getting better at detailing the panning with better fitting and fastening and it's rare I find one substantially under-performing.

Don't get me started about the Leakage to Outside test....

I have never seen an inside wall that did not leak to the exterior. Go ahead talk about the leakage to outside test.

Busy days

"I have never seen an inside wall that did not leak to the exterior."

I have noticed some top plate leakage at a handful of walls in some homes but certainly not enough to make a blanket statement about "all" walls. I wish I could have new home builders do attic air sealing the way we do in existing homes - spray foam ALL penetrations from above, including top plates. This is super effective but doesn't fit in at all with the way builders do new construction around here (Wisconsin). That said, the top plate leakage I do see does not rise to the level of failing the homes in our program or result in discomfort that homeowners might feel. Would I like them to do a better job? sure, but production builders in a tight market just are not going to justify that cost.

As for the LTO test, I should have specified that I feel it's a bogus test when all ducts are located inside the thermal envelope and the house is testing tight (<.2 cfm/sq ft). After having done a couple hundred of these tests and coming back each time with close to to zero leakage (basically unmeasurable) I came to resent the fact that we were doing this test just to be able to check a box to get the tax credit and charging the builders for the extra work.

Putting all the ducts inside is a great option that should always be done but I felt that the builders were not being rewarded for making this good design choice. I'm open to data that shows there is a compelling reason to do this test in this situation. (Note: I do think the test is very useful for systems with ducts located outside the TE)

Of course it's a bit moot now that the credit has expired, and likely not coming back in it's old form.

Mark -- you are right I should not have said never. The only walls that I have seen that do not leak to the exterior are houses built with airtight drywall. Since you have not seen leakage from interior walls I wonder why you seal at the top plate.

The purpose of the leakage to outside test is to prove that interior ducts are really interior (sometimes they are not).  Based on your response I presume you are taking into account the higher pressures when these cavities are used as returns or have leaky ducts in them.

If the total leakage is low then the leakage to outside test it is unnecessary.

Tests in multiple states show there is a significant difference between total duct leakage and leakage to outside. For example a study in Arizona found the average total leakage for 28 systems was 310 CFM25 (574 max) and average 193 CFM25 leakage to exterior. 

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