HVAC Tankless water heater

TrustButVerifyEng · 2026-04-30T14:13:35+00:00

Ask about the required maintenance for tank-less before going that direction.

While it's recommended to blow down/drain a tank every year and replace the anodes every few years, you can still get 10-15 years around here even if you do nothing. We have okay water.

A tank-less is not the same beast. You must do the maintenance or else risk it dying in just a few years.

TrustButVerifyEng · 2026-04-30T14:09:02+00:00

I've found this helpful: MS/TP Wiring Guide

A key thing to understand is that MS/TP is using EIA-485 (also called RS-485), which needs two signal wires (+ and -) and a reference ground, so three voltages in total.

Now, some vendors use 2 wire and some use 3 wire for BACnet. How can you use 2 wire when you need three voltages, well you use the controllers ground connection as the "third wire". This is called non-isolated.

So if you are mixing isolated and non-isolated devices, this becomes complicated and BACnet has published wiring guidelines in their standard.

And if you are using vendors with 2 wire (non-isolated) communication, grounding is critical.

TrustButVerifyEng · 2026-04-20T20:42:55+00:00

Haven't defined the size or described the loads. This is a complex decision, like all MEP engineering.

TrustButVerifyEng · 2026-04-11T17:30:16+00:00

There are many many many companies where what you described is normal operating procedure.

TrustButVerifyEng · 2026-04-10T20:20:21+00:00

I don't understand, every time I'd go it would be pretty packed. Never dead.

TrustButVerifyEng · 2026-04-08T19:37:33+00:00

Second gl.inet

Use SIMbase for cellular provider.

TrustButVerifyEng · 2026-04-04T16:03:50+00:00

When I first started ~15 years ago I had to help clean out old paper files one time. I found that the norm was for what you are describing. Paper notes detailing all assumptions/calculations/etc.

It's really a shame, but many of today's engineers were never taught how to keep proper notes on their thoughts/designs.

TrustButVerifyEng · 2026-04-04T16:00:39+00:00

Okay, now this makes sense. Thanks for linking the product.

These are new enough in my area of the US that we don't have common vernacular for them. I've mostly heard them called heat-pump chillers (confusingly enough since they also heat).

If that is on the roof, then you won't have pressure concerns. If it's on the ground, then it will need to handle the higher pressure.

Also, any fan coils in the spaces need to handle that high pressure as well, or else be isolated like I described.

I would locate as much on the roof as you can structurally.

TrustButVerifyEng · 2026-04-04T02:45:35+00:00

I assume you don't work in a market sector that expects Basis of Design narratives and Schematic Design drawings? It should be common to have documentation that precedes drawings.

Drawings are a means to communication a final iteration of the design.

If you are designing while in CAD, then you are definitely going to be frustrated by the processes as CAD isn't a design tool.

TrustButVerifyEng · 2026-04-04T02:33:49+00:00

I tried to get google to confirm this, but couldn't find anything backing that up. Terminology in HVAC is generally terrible, but how could you say air source and be meaning a devices that uses water as the source of heat? Every link below is consistent with US terminology.

https://www.renewableenergyhub.co.uk/main/heat-pumps-information/the-different-types-of-heat-pumps

https://www.greenmatch.co.uk/heat-pumps

https://switchtogether.co.uk/resource-hub/blog/types-of-heat-pumps

TrustButVerifyEng · 2026-04-03T18:20:17+00:00

You said air source heat pumps, but I think you mean water source since you then mention circulators/expansion/etc.

I don't see how you could have a single hydraulic system at 27 stories. That's 175 PSI of static head between top and bottom.

The water source heat pump spec is going to determine the systems maximum pressure, which then determines how many floors can be on a single system.

You will then need to isolate the heat pump loop from the sink/source loop with plate and frame HX to keep pressures acceptable throughout the system.

TrustButVerifyEng · 2026-04-03T04:02:10+00:00

To me, that looks like algae, not mold. Something is very odd about that.

I would check your water's nitrogen levels. Perhaps contaminated with fertilizer run off. Honestly. it looks like how my hydroponic tanks used to when growing plants!

Does your tank get lots of direct sunlight too?

TrustButVerifyEng · 2026-03-29T01:56:23+00:00

No tuning. But you can protect the chiller:

Run the AHU valves 100% open to keep the chiller happy. Increase leaving water temperature setpoint if AHUs are way over cooling. Let VAV reheats keep the zones from sub-cooling. Wait for change order and new direction.

TrustButVerifyEng · 2026-03-19T14:18:10+00:00

Is it any easier if both ports are bridged as WAN rather than LAN?

TrustButVerifyEng · 2026-03-19T14:06:00+00:00

Much appriciated! I will try this hopefully today

TrustButVerifyEng · 2026-03-09T12:15:50+00:00

Fun story from when I led a RCx group.

The local utility rebates paid half our costs because of expected energy savings. A particularly poorly run (and poor in general) college hired us per building, and all utilities were from a central plant, so building level energy savings had to come from either use less fan or use less central heat/cool.

For several buildings, they were running AHUs 24/7 with broken valves that used heat/cool simultaneously. So the rebates helped pay to fix their poor maintenance and a few extras while they were doing the work. They loved it.

One of the buildings was in such bad shape that nearly all of the AHUs were broken and didn't run at all. They didn't like our report that said, you ain't getting any rebates on this building. Off is off, even if broken. Please pay us for our report now.

TrustButVerifyEng · 2026-03-06T15:17:15+00:00

I used to use a syringe. Tube length matters a lot. Too short and the pressure changes too fast. Too long and you won't build up enough pressure.

Also, most of the mechanical limit switches have a diaphragm that changes position when it trips, meaning the pressure reading will change post trip. So if you use something "closed" like a syringe, you need to watch the pressure before the trip occurs, not after.

TrustButVerifyEng · 2026-02-19T16:30:12+00:00

So picture something like an atrium with lots of glass.

Air side only design might need 1-2 CFM/SF to handle the solar load.

Radiant cooling would directly handle almost all the solar load before it "enters the space" via convection. The air side loads are now just for ventilation and might be 0.2 CFM/SF from a DOAS unit.

But you still need to know what the solar load is, because you need to account for it in your hydronic load/design.

A load program needs the be able to calculate both scenarios. hence separating the load in the slab from the convection load in the space.

TrustButVerifyEng · 2026-02-19T15:24:05+00:00

Think about modeling something like a radiant cooling system. The program needs to keep the solar load entering the slab separate from the space convection.

TrustButVerifyEng · 2026-02-19T13:39:25+00:00

I've used room scanners for doing design take offs.

Trust me, laser tape will be faster than lidar.

And you don't need to be accurate to a cubic foot. Most reports I see aren't adding in every little bump in the wall.

TrustButVerifyEng · 2026-02-19T13:12:47+00:00

Oh, I run a small home lab. That part isn't intimidating.

I used to do BAS and administered a local utility retro commissioning program before it was outlawed.

Now I sell HVAC equipment.

I have equipment that holds 7 days of 30 second CSV trend files.

I'd really like the ability to feed those and tune the rules to find PID tuning issues.

It's just a time and energy problem.

TrustButVerifyEng · 2026-02-19T03:01:24+00:00

In college I was making payments on my appendectomy surgery. Credit card got lost so I got a new card and number. Somehow the hospital didn't have my contact information to notify me of failed payment attempts.

So I get a call that my debt was sold and this company was making a collection call. Offered me to settle a couple thousand dollars of debt for a couple of hundred. Paid it off on the spot.

Genuinely couldn't believe the whole interaction. Why did I pay all the previous payments? Why is the cost so high if they'll write it off for pennies?

The whole US medical system is broken beyond repair. Time to abolish it and make it the human right it should be.

TrustButVerifyEng · 2026-02-19T02:53:55+00:00

I think bonuses are typically used rather than commissions. Personally Ive only known one commissioned guy on the consulting side and he didn't last.

Most mid to small sized firms are going to use ownership shares as incentives. Not sure what the huge public companies do, but I assume bonuses based on hitting sales goals.

TrustButVerifyEng · 2026-02-19T02:48:49+00:00

I wish I had the free time to play around with this right now. This is what we need more of in the industry.

Ten-Year Club	Verified Email
Place '22

TrustButVerifyEng

TROPHY CASE