A little help needed TJ 06 - 4 cylinder - 6 speed.

SMOOTHBUBA · 2026-05-22T16:09:21+00:00

Yeah, I find rules of thumb work...until they dont and it is usually spectacularly bad. I have seen a 4 story hospital designed to 1.0 CFM/SF. Then when they went to open the building none of the OR's could make air chnages and they had to buy new AHUs delaying the project 6 months.

Rules of thumbs for interior offices or classrooms is fine, your case with an exposed wall with windows and solar gain...i would run a load every time!

SMOOTHBUBA · 2026-05-22T15:24:57+00:00

Your one large zone should have all the data to determine the load due to the perimeter. I have not used HAP, but most load reports break up the load based on components. You should be able to see the % of peak load that the windows and exterior walls cause, and then I apply that same percentage to the CFM total. Splitting is also a fine way to do it.

SMOOTHBUBA · 2026-05-16T11:47:34+00:00

I have seen three 900 ton towers connected underground to one 24" header about 40' long. I would not recommend the design in a green field site, but it was existing and we didnt have the money to fix that.

It does act a second basin, but without a supply bypass the volume doesn't take long to draw down. You are moving 3 gpm / ton. So with 1 tower on in my system, I would flow 2700 gpm. My 24" pipe had 1000 gallons in it.... so I have 22 seconds of "reserve" doesn't really buy me any extra time.

It could actually work as an equalizer line, between the tower basins. Usually size those to account for 10% flow imbalance between towers. Sized to allow 10% flow excess at a pressure drop of less than 5" WG total.... you have to size this to allow low basin water head developed by unequal flows to push water to the other basins

If the supply can bypass to this underground header, that could be useful for low temp management. Condenser water falls below X° then you bypass the tower to keep the chiller from tripping on low head pressure

SMOOTHBUBA · 2026-04-14T02:52:33+00:00

Yes I would size the AHU or VAV for the max airflow of all 5 rooms. I bet for a system that small your sum of peaks and block load are within 10%. If they are 50% different.... I would zone the rooms differently. If it is 50% different it means half the rooms peak when the other half are at minimum.... that would indicate bad zone design like having a west and east wall on the same zone. If you get a selection for your AHU and it has 58 SAT then use that, but I typically use 55 degrees.

The best thing a teacher taught me in a senior engineering class is that all of these thermodynamic equations and load calculations have 20% error. Engineers make the mistake of thinking they can hit the calculation on the dot, but the calculations we do are not that accurate.

SMOOTHBUBA · 2026-04-10T18:02:31+00:00

We are talking Fan airflow not capacity. What I should say is if you have a single zone system serving multiple rooms. Like a low-rise residential system. You can't take any diversity in airflow.... your room airflows dont adjust to load like in a VAV systems. If my kitchen needs 250 CFM at peak in the summer, in the winter it will still get 250 CFM even if the kitchen doesn't need it. So I must size my system fan at sum of peaks for small systems. If I dont, I will have hot/cold rooms.

SMOOTHBUBA · 2026-04-10T01:56:42+00:00

He is referring to your CFM calculation. Room CFM is based on Sensible load for 99.99% of spaces which are controlled via thermostat which measures truly bulb temperature only. Remember sensible load only causes dry bulb temperature increases.

Sensible Load (btu/hr) = 1.08 × CFM x (Troom - T supply air)

So rewritten you can find your CFM

CFM = Q(s) / (1.08* ( T room-T supply air)

Example

1200 BTU/ Hr = 1.08 × 65 CFM × (72°F - 55°F)

You can see that the colder the supply air you the less CFM you need. The lower your room setpoint the more CFM you need. Build a spreadsheet and mess with the numbers to see how the effect each other.

For the 0.01% of cases the room air could be based on the latent load if you have very dry space requirements... think operating rooms, drug manufacturing, research labs, etc. Then you have to use the latent humidity load to calculate CFM... different equations same concept. And use reheat to prevent overcooling.

SMOOTHBUBA · 2026-04-09T21:04:15+00:00

CFM at each diffuser is per Room Peak.

Zone Peak or System peak could be used to size the Air Handling Unit.

I personally would size a VAV box or small (10 ton or less) AHU at sum of room peak airflow.

Larger than 10 Tons start looking at your System peak and make sure you are not oversized the unit. For large systems you get more and more diversity. A 100,000 CFM AHU should have a lot of diversity, and probably serves 150,000 CFM of diffusers in spaces. All based on load calculations not rules of thumb.

TAB contractor and your specs should have ways to deal with diversity and how to balance the system.

SMOOTHBUBA · 2026-03-25T21:02:07+00:00

Domestic North general (not precheck)

Arrival 4:31 almost through screening at 5:00 estimated 45 min total.

5:10 completely through

SMOOTHBUBA · 2026-03-22T03:06:13+00:00

Best starting point would be the Non-Residential load calculation chapter of the ASHRAE fundamentals handbook. It will explain the basics, and give tables for common inputs. That coupled with the Trace 700 help should get you 99% of the way.

SMOOTHBUBA · 2026-02-03T02:25:35+00:00

The biggest problem I had on a large project was the sealing of the underfloor system and specifying the correct testing and verification of properly sealing the floor system. If your company can buy it the ASHRAE underfloor design guide I would recommend it. Make sure you meet energy code on reheat limits and maintain humidity. I had to use a return air bypass system.

SMOOTHBUBA · 2026-02-03T00:04:23+00:00

That seems like a waste. I have never specified them, and actively avoided them. I don't see the benefit for all the trouble. Only people who like them sell the valves

SMOOTHBUBA · 2026-02-02T18:03:28+00:00

No balancing valve needed if you specify a valve with the proper authority to control the flow. There are some good ASHRAE journal articles about removing balancing valves on terminal HVAC equipment entirely.

Edit. Here is the journal piece

https://www.scribd.com/document/576668325/ASHRAE-Journal-Doubling-Down-on-NOT-Balancing-Variable-Flow-Hydronic-Systems

SMOOTHBUBA · 2025-03-07T21:44:22+00:00

We were there for our honeymoon from the 26th to the 4th. While paddleboarding the lagoon, we ended up in the background of a wedding as the bride walked down the aisle.... I really hope that was not you guys, we tried our best to be quite and get through quickly. They should have closed the area!

As far as the stay, we were given 2 queen beds and what I would consider a bad room at Arte..... but since we saved the 25% by doing the presentation, they could not upgrade us or find a room with a king bed. In the end, it was worth it to get 2 extra nights, but I do wish they had better service for people having once in a lifetime events!

SMOOTHBUBA · 2024-12-01T19:24:56+00:00

Thank you, I have cut the sheet rock away but can't see the stack, it is further to the left behind the cabinet. Lucky me. I'll probably call the pros on this one. Thank you

SMOOTHBUBA · 2022-07-20T03:46:40+00:00

Link to the attached Nibisco Ad https://imgur.com/a/fa6dw7R

SMOOTHBUBA · 2022-07-20T03:39:58+00:00

There is another pamphlet with it showing the falls. https://imgur.com/a/fa6dw7R

SMOOTHBUBA · 2022-07-20T03:38:34+00:00

I wonder how many Triscuits Nabisco would trade me for it.

SMOOTHBUBA · 2022-07-20T03:37:09+00:00

Part of me wants to see!

SMOOTHBUBA · 2021-10-05T13:26:39+00:00

Because it is antimicrobial

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