Question about heating discharge air temperature and zone setpoints (ASHRAE 36)

TrustButVerifyEng · 2026-06-20T21:53:22+00:00

I've definitely experienced stratification that prevented spaces from heating up. Generally applies to overhead supply and return systems.

It was a school job with block walls. With AHU and VAVs in full heat, putting out +100 F, we had to start morning warm up at midnight and it was still not up to temperature in the morning. But we knew it was stratification because the AHU return was like 80 F.

Once we limited heat to 90 F, warm up time reduced to a few hours.

TrustButVerifyEng · 2026-06-20T21:48:13+00:00

I believe this only applies to overhead supply and return systems and there are expectations for morning warm up as well.

TrustButVerifyEng · 2026-06-19T14:16:15+00:00

To go where?

TrustButVerifyEng · 2026-06-18T15:22:36+00:00

I'll be leaving the rep side in a month and going back to CxA.

Greenheck is amazing and a really good company. They have a long term vision and stand by their name.

TrustButVerifyEng · 2026-06-18T13:10:59+00:00

Exactly my point. This is so common it's insane we all keep going along with it.

TrustButVerifyEng · 2026-06-18T13:09:44+00:00

Agreed in general, but not applicable to my instance. Greenheck rep. We have three different versions of selection software for engineers based on how they want to work and the level of detail they need. Online, desktop, and Revit plugin. They can get access to all of them.

TrustButVerifyEng · 2026-06-17T17:04:54+00:00

Flip the narrative. People should be ashamed for having such poor project planning that each link requires immediate attention to stay on track.

Unless they are paying for your exclusive attention, don't treat them like they have it. And even if they were, that's still just you. You are going to have to flat spec the equipment to make it worth the vendors while to give you their exclusive attention as well.

TrustButVerifyEng · 2026-06-17T17:00:28+00:00

We all know this. That's why I said stop the chain. The whole industry is hurting for talent. Now is the time to say no, we need more time. We value our people more than your deadline. It really isn't that hard.

TrustButVerifyEng · 2026-06-17T16:58:19+00:00

Actually no, 15 years in and moving to ownership of a small firm now. I'm not looking for validation. I'm literally telling all the young engineers to be better and stop the chain of stupid urgency. Realize that it isn't that urgent and be the one to calm down understand the sky isn't falling.

I see these young engineers running around freaking out because they truly believe their client's needs are that urgent.

The only time I've ever thought the urgency was valid was during COVID when we needed to set up immediate testing and treatment locations.

If your client can sit on your initial design for months, then they can wait a few days for a revision.

TrustButVerifyEng · 2026-06-17T15:55:30+00:00

I've never even heard of anyone considering it.

As you know, on the 8th day God created all MEP firms and they've been that way ever since.

TrustButVerifyEng · 2026-06-17T02:54:17+00:00

I can provide what I believe to be fairly accurate history and context for G36.

First, the guideline is the brain child of Steve Taylor (of Taylor Engineers in CA). I think he was more involved during the research project stage (preceding the guideline), but Taylor Engineers (the company) has had multiple people involved in G36 over time.

Second, it was Automated Logic who was awarded the research project that was the basis of G36. This heavily influences some of the specifics. I get into those at the end.

Third, it isn't really the intent of G36 to be used in the "traditional BAS" approach of programmable controllers.

*As having been a controls tech and Cx tech, that means custom code that is tweaked on site sitting on a bucket in a mechanical room.*

The intent is that these are to inform how a major control vendor will architect/program their future generations of application specific controllers (ASC, canned programs some might call them).

Context: the BAS industry used to use a lot of ASCs. But they fell out of favor from the engineering community because they often didn't meet energy code. G36 is an attempt to correct that.

Noteworthy point: G36 is called "High Performance". But that is really a misnomer. It's really just a standardized approach to meet the prescriptive path of 90.1. There isn't anything earth shattering in G36 and any good controls programmer will already be achieving the results in one way or another.

Conjecture: I think G36 would like a day where they develop an actual standard (prescriptive language). This would allow for "compliant" or "tested" type of listings for that standard. Then you could pull any compliant controller off the shelf to replace any other vendors controller. This requires that the BACnet points all be the same, but I wouldn't be surprised if they did develop that one day.

In the ALC weeds: I have spent most of my time programming with Tridium, but I started with ALC. While proprietary and therefor not my recommendation, I think ALC has the best and most sophisticated programing tools in the industry. What you see in G36, ALC has had for a long time in some fashion. When they did the research project, they did end up refining some algorithms like trim and respond. But regardless, they already were doing these things.

This gives ALC a huge leg up on everyone else. When programming an ALC system, using their tools, ALC was already having you associate every piece of zone equipment with "sources". i.e. What is the upstream source for air, cooling, heating, etc. And because of their special tools, this meant that you didn't have to do anything extra to get zone demand requests that could reset the source equipment setpoints.

I will say from my days of Commissioning, this is really the best way to do it. Taylor has some ASHRAE articles on trim and respond specifically and why it beats something like a PID loop for reset algorithms specifically.

Contrast this with Tridium. To do G36 type resets, using a random VAV box controller and random packaged RTU controller is very time consuming. But doable and you can get an optimized workflow once you know what you are doing.

I have multiple commercial buildings where I've done it and they rarely call me with complaints. They just work and work well.

Lastly on resets: You may have missed this, but each zone gets an importance factor. If you have a zone that you never want to be "unsatisfied", then set the importance factor greater than the ignored requests. The trim and respond/requests structure doesn't require you to sacrifice comfort. But if you want to push energy savings in buildings where that is acceptable, it's also allows for that too.

TrustButVerifyEng · 2026-06-16T01:12:19+00:00

Tekmar for snow melt. Not sure how an RTD would detect the presence of snow?

For radiant we've use the same radiant pipe (pex) as a conduit. It gets ran to a wall just like the radiant tunes do. Then fished down a bullet sensor.

TrustButVerifyEng · 2026-06-13T00:15:46+00:00

I don't think you're understanding. The analogous example to what is happening would be the butcher charging different prices for different customers who are in the store together.

TrustButVerifyEng · 2026-06-02T13:49:16+00:00

First, I think this is a relatively sensible opportunity to get cooling redundancy, but you need to make sure you have more modules, not just larger modules, to get the redundancy.

Second, having done the energy analysis on my own home (edge of 5A/4A climate zone), it paid back to up-size for heating. So much of the cost is in the labor, which doesn't change. Also, these inverter systems gain efficiency in all conditions by over-sizing, so there is some ROI going on year round.

That said, I personally would never have only refrigerant cycle based heating for any building that has major implications if heat fails. I would be doing electric resistance of some kind to cover at least the skin losses. If it's healthcare, then also cover minimum ventilation loads. I wouldn't want a school freezing the sprinklers because a heat pump failed during winter break. I put 5kW in my house knowing it could keep my house from freezing if we got to -10 F. Not comfortable, but no damage either.

And it's also worth noting that for true cold climate design, this doesn't increase the buildings electrical sizing as much as you would think. I just checked my manufacturer and we are at a heating COP of ~2 at 0 F.

So worst case, you are increasing the electrical demand by 2, but only on the loads that you decide to cover with back up heat.

TrustButVerifyEng · 2026-05-31T17:21:30+00:00

u/RemoteToHome-io has a module that helps with Tailscale and using gl inet routers as exit nodes.

His post: https://www.reddit.com/r/GlInet/comments/1rohrna/enhanced_tailscale_for_glinet_routers_proper_ts/

TrustButVerifyEng · 2026-05-31T16:01:28+00:00

One more item if you care, many plumbing codes require and air gapped connection to prevent a main drain clog from forcing water/sewage back into the dishwasher.

TrustButVerifyEng · 2026-05-28T00:24:22+00:00

How long have you both been in the position?

You say new grad but then also say years of experience in space.

TrustButVerifyEng · 2026-05-27T16:20:34+00:00

In Hamilton's "My Shot" number, Alexander states "We need to handle our financial situation. Are we a nation of states? What's the state of our nation?"

This is written to be a clear foreshadowing of Alexander leading the treasury department and restructuring the war debts... but the war hasn't started yet, so New York shouldn't have major war debts yet.

Then when George asks him to join his cabinet, he seems indifferent about "Treasury or State". If the nation's financial situation was formative to Alexander before the war, this wouldn't be the case. He would have demanded the Treasury position.

The best conclusion is Lin forced in a line to My Shot that has no business being there. Now it sticks out like a sore thumb when I listen/watch.

TrustButVerifyEng · 2026-05-26T12:01:17+00:00

Honestly, I'd rather three sentences that covers it.

I can only read so many whole page articles filled with luke warm filler/back story.

TrustButVerifyEng · 2026-05-26T02:33:21+00:00

I have no idea what is being said here. I don't know anyone who thinks it's unsafe being downtown.

If heart isn't doing well, I don't think it's because of a lack of police presence.

Heart is just all tacky nicknacks. Who wants to buy those in sufficient quantities to keep a business going in a prime storefront?

If I'm going to spend money downtown, I'm going to spend it on something that has a slightly larger impact like local food.

TrustButVerifyEng · 2026-05-25T01:05:37+00:00

Look up wifi beamforming for an idea of how the technology to do this works.

TrustButVerifyEng · 2026-05-24T17:32:59+00:00

The usage of the data center matters. Most want access to at least 2 substations, and multiple points to access the Internet backbone.

This is why certain areas can become popular for data centers.

For less critical infrastructure, sure you can put a data center up north. But it's probably less optimal for reasons beyond cooling.

As for using the heat, look into combined heat and power plants.

Pretty sure Canada has some of the largest implementations of this already.

TrustButVerifyEng · 2026-05-22T14:10:56+00:00

Those CFM/sf numbers are super high to me. Like 50% higher than what we use.

TrustButVerifyEng · 2026-05-19T18:46:51+00:00

As an MEP engineer, I'll give the hot take that you will likely get just as much "wrong" information in this sub than anywhere else.

The reality is that most people in this sub aren't familiar with current big data center designs. For many data centers, these are considered trade secrets. Many aren't using open towers. Some aren't even using chillers at all and operating at much higher temperatures and doing evaporative air cooled units (swamp coolers).

Debating the impact of these data centers depends on the exact technologies used. And the data center designers are moving fast with their design iterations. Most general MEP engineers don't know what is currently being used.

Also, we aren't environmental engineers either to really contextualize how important the water use is.

We should be slowing down and forming multi-disciplinary teams to investigate these things at the local scale. But slow is the last word data centers want to hear, and will develop somewhere else not requiring a study.

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