Advice needed on longest lasting heating/AC systems for new school building

delcrossv

A board of a private school I'm advising is looking to build a new campus for 500-600 students.(90-100k sq/ft) We'll be under a 100 year land lease with a probable purchase option at the end.

Point is, we can do a big campaign to get it built, but need a system that will last for an expected building lifetime of 75-100 years. Odds are we'll only be able to tap the major donor keg once and major system/ building replacements later would be a cashflow problem, disruptive to classes etc..

So what's the board's opinion on what to choose for a HVAC for very long term use?

Hydronic radiant baseboard piped in black pipe with a standard ducted AC system for cooling and air exchange? Chillers? Something else?

Everyone knows boilers etc won't last forever, so we can plan for that, major repipes/ whole system replacements are what we're trying to avoid. So more cost up front is fine, as long as the running cost is low over the long term.

This will all be gone over with the architect/ design engineers, but I'm looking for an initial point of departure for the discussion.

EBEBRATT-Ed

If your in a cold climate I would do hot water perimitter heat with mod con boilers which could also heat your DHW. Heat pumps for each area will bring in fresh air and can be used for heating in the spring and fall & cooling in the summer. I would include energy recovery ventilators schools need a lot of ventilation especially in these Covid days

pecmsg

Schools are a special bread with crazy requirements. You must consult an engineer. 

Solid_Fuel_Man

The 2 new construction schools I have worked on have hot water heat. 

One is with multiple oil fired boilers, the other is with 2 oil boilers and one wood chip boiler. 

One have radiant slab throughout the other has univents in each room. 

The one with radiant slab, has several large ERVs with ductwork above the suspended ceilings. The ERVs have some fin tube coils to supplement the radiant is needed. These are both in climate zone 7. 

Personally....I hate univents, so many damper actuators and moving parts in every one. But there is little to no ductwork. With a ducted ventilation at least the moving parts are all in one mechanical room. 

As far as radiation is concerned, as long as there is no rubber seals involved it should last many many many decades. I'd spec only soldered, thereded, or welded pipe connections. No VIC, and no press. Those are for fast installs, not long lasting ones. 

YMMV

hot_rod

Ground source HP if you want efficiency and have electricity as an option. Plus land area or bore hole space.

Some perimeter emitters, panel rads instead of fins to keep a cleaner emitter. Air handlers for filtration, humidification, etc. HVRs possible for handling the ACH.

The engineer needs to think low temperature, not to exceed 120F requirement on design day. This allows best efficiencies with mod cons air or ground source heat pumps. Future proof the distribution with low SWTs.
I think by now the jury has decided that plastic or pex tubes or PP will last as long as steel pipe without all the corrosion issues and labor costs.

Jamie Hall

I completely agree with @hot_rod . Further, may I suggest that you contact Carleton College, Northfield, Minnesota and seek comments on their experience. They recently commissioned a campus wide ground source heat pump system replacing a combined steam and hot water system -- in a very cold climate.

JUGHNE

The newer addition to our school uses RTU's.
The good thing is they take up no inside floor space.
Maintenance all done outside, change out does not disrupt inside activities.
Economizers and fresh air intake. All ductwork above the ceiling.
Perhaps some have HVR's built in, better to be a separate unit IMO.

Our problem is that they planted one giant RTU on the roof and rely upon zoning for too many rooms. The control system for this has been a nightmare.
In 1997 the HVAC engineer designed this mess with the capability to monitor and adjust things remotely.

This ME had never heard of a 4 ounce gas pressure system and insisted that 2 PSI piping sizes would work. After all he was close to god himself.

All of this was over everyone's head, including the installer.
They were about 100 miles away and would not come here until the warranty expired.
IMO, they could have installed more RTU's and less ductwork, all with simpler controls.
One compressor down will really cut into the cooling capability.
Multiple smaller units can get you by.

We of course have a predominate heating season, but with school approaching year round use, cooling is a major issue.
With your student count you will probably need almost cold weather cooling.
Even with LED lighting internal gains are higher than one imagines.

Of course insist upon a roof hatch from the interior.
The is a freeze proof roof water hydrant which will help to get the coils attention.
For that size of building maybe two of each.

Without a roof hatch, air filters will get beyond maximum run time and coils "might" get cleaned.

ME's and architects never had to do these jobs in their life and assume a ladder and hose over the top is a simple task. But 2-4 times a year??

(Hopefully you don't think I have an attitude toward these professions...sometimes... maybe )

But RTU's are not very high in efficiency or longevity as I remember. Maybe there have been improvements.

Perimeter hot water heat would be good and require less use of RTU's.
A friendly piping tunnel around the perimeter would be useful for many purposes.

But what boiler? ModCon certainly have the AFUE number, only with low return temps. And then maintenance costs and longevity. That discussion goes on here on the wall.

One thing I have learned working for intuitions is that admin and custodial personal change.
Both are always looking to trim the annual operational budget.
The new person may look at what was spent in the past and their logic is that every thing has worked and why do we need to spend this money now.

The custodial people will say I can save this money in my budget and perform this maintenance myself......when I have spare time.....and that doesn't happen.

So the best system is one that can be neglected for at least 2-4 years and not kill itself. Just stop working to get attention.

An old 1932 school with steam heat that was just decommissioned this fall was replaced by a new building with Geo-thermal HP's.
The custodian told me yesterday it was working somewhat but still control issues (WIFI BTW) they were working out....after 5 months. Wait until they switch over to cooling or mixed use. This bright guy will get it figured out and then maybe change jobs in a year or so. Then they start over with a fresh face at a minimal wage.

So I would consider all of the above, IIWM.

delcrossv

Thanks everyone for the helpful comments!

@hot_rod SWT's ? A little help for the acronym allergic please. 😀

I'm liking the perimeter HWH radiants (no fins) like baseray or something newer. Old building had HWH forced air units, noisy and a maintenance nightmare.

Radiant is great, until it's not. Having to chip up a floor would be a killer cash-wise. I'm thinking above the slab emitters is a safer bet. Piping raceways would expedite maintenance. 👍

Re: PEX, I'm not sure that's code for schools here. (I've never seen it)

Not a fan of Rooftop units, @JUGHNE (they still are pretty unreliable). So either a central unit or distributed coils ?

As it's leased land I doubt we'll get permission for a borehole, so that kills ground source HP's. (would be nice)
Design day is 0 degrees here.

JUGHNE

SWT is supply water temp....my best guess. The lower it is the more emitters you need.

Another positive for RTU's is that both the outside and inside components that fail are outside.
I hate them myself and have stopped working on any.

In any event you will need AC, fresh air and the economizer feature is good if you are in a fairly dry shoulder season and need "free" cooling.

tim smith

What climate are you in to start with. Design temps?

tim smith

Summer design?

delcrossv

tim smith said:

What climate are you in to start with. Design temps?

See above. North edge of 5A, 0 degrees design day.

hot_rod

delcrossv said:

Thanks everyone for the helpful comments!

@hot_rod SWT's ? A little help for the acronym allergic please. 😀

I'm liking the perimeter HWH radiants (no fins) like baseray or something newer. Old building had HWH forced air units, noisy and a maintenance nightmare.

Radiant is great, until it's not. Having to chip up a floor would be a killer cash-wise. I'm thinking above the slab emitters is a safer bet. Piping raceways would expedite maintenance. 👍

Re: PEX, I'm not sure that's code for schools here. (I've never seen it)

Not a fan of Rooftop units, @JUGHNE (they still are pretty unreliable). So either a central unit or distributed coils ?

As it's leased land I doubt we'll get permission for a borehole, so that kills ground source HP's. (would be nice)
Design day is 0 degrees here.

Radiant slabs especially are not a good match for spaces that see wide and often occupancy load switches. Churches are another example. Too much flywheel effect, too many 400 BTU output humans.

If budget was not a concern some of the radiant ceilings and or chilled beams are very nice systems. Quiet, clean, hidden from view, lots of available surface areas on the ceiling, so very low SWT for heating, higher chilled water temperature requirements = easier lift with GEO. Google chilled beams.

Some nice commercial A2WHP systems coming out. Daiken, Mitsubishi, etc.

tim smith

Perimeter radiators, coupe boilers. heat reclaim air to air Mitsubishi’s city multis with non ducted wall heads with fresh air intakes. Gives you the supplemental heat fo 0 temps although very likely would not need it, but….. also would give a way to toggle to low carbon or carbon energy. Maybe throw up 50 or so kw of solar to offset some usage. Might be 20 or so 10 ton outdoor units and x # of wall heads. Include some hot water modules off outdoor units possibly too.

delcrossv

@tim smith Solar's kind of a wash here. Too little insolation, too much maintenance cleaning snow off collectors. Those Mitsu units look interesting, Thanks!

chief

Hello, I am the chair person of our school district facilities committee. We have completed a couple of HVAC up grades to our facilities. We are in Wisconsin so see some cold temperatures in winter and hot humid days in summer. 

We have chosen central air handling units and then variable volume boxes for each room. Central chilled water units provide cooling for the summer months and allow for greater control and efficiency. The air handling units are installed in penthouses or mechanical rooms indoors. This provides a good environment for the equipment as it is not exposed to the extreme elements. The same for any service person that has to do maintenance on the equipment appreciates that it is not on the roof on a -20 degree day.

Heating is provided by high efficiency boilers with perimeter radiation along outside walls. The variable volume boxes all have heating coils in them for keeping the room at the set point. The central air handling units have heating coils to allow for outside air to be brought in and tempered to provide the required make up air. 

All systems are engineered by a local architect or HVAC contractor depending on the size of the project. Lower supply water temperatures can be designed if your facilities are new. This would allow for condensing boilers to be used year round and would increase overall efficiency. 

A good ddc contractor helps in control of all the equipment as well. Outdoor lighting can be incorporated on the building automation system too. 

Having a quality HVAC contractor as a partner in an ongoing preventative maintenance program is key to keeping it operating efficiently as well. 

Some of our systems are 50 years old. The air handlers are running fine and the VAV boxes are in good condition as well. The boilers and chillers have been replaced as needed. Our district has 3 campuses. Largest facility has approximately 700 students. 

  Hope this helps. 

delcrossv

@chief Yes it does! Thank you. How much of an efficiency gain do you realize going with central chillers?
Coils in the VAV boxes or in the air handlers?

I see you temper intake air, any heat recovery or did that not make sense economically?

retiredguy

I am not going to recommend any type system since I have been retired for almost 15 years and so much has changed. I grew up in the heating business servicing the boilers in schools, hospitals and industry. The more simple the system the less maintenance it needs. The systems that lasted the longest were heated with pumped hot water, steel piping, cast iron rads or steel finned uni-vents, with multiple cast iron H B Smith or other name brand boilers. I know of numerous systems like these that lasted well over 100 years. The next longest lasting systems were steam systems with the same listed components as the hot water system except the piping was wrought iron which is no longer available. That was yesterdays system. Today high efficiency is in vogue. I would recommend that you contact as many school systems as you can that have the same climate as you do and ask what systems they have and how satisfied they are with those systems. The ones that I talked to were happy to share their experiences. You can find out what worked for them and what did not.

Then hire the best architect and engineering firm you can. I would not want one company to do both and hire a good job superintendent (we used to call them a clerk of the works) also from a third company. Remember this, the more complex the system, the more service it will need. I saw the good, the bad and the ugly over my 40+ years. Do not buy the bad or the ugly.

ratio

I would avoid any type of VRF system if I were planning on long-term operation. From my experience, they don't seem to last much longer than any other type or refrigeration, yet you're locked in with the refrigerant piping—better hope it meets the requirements of the replacement system! They're also evolving at a pace that may very well have several generations in that same cycle, another gotcha when making repairs or upgrades. (We've had to give away heat pumps, albeit mini splits, because of that fact.)

delcrossv

@ratio Thanks. VRF isn't gonna fly for this. VAV or some other type of chilled water seems the way to go.
I'm not sure we can hold dewpoints steady enough for chilled beams. Interior raining being a "bad thing". 🤣. I'm going to do everything in my power to kill univents too. I really can't stand them.

hot_rod

I agree you have way more options now and down the road with a hydronic system compared to VRV.

There are examples of chilled beam, radiant ceiling and radiant floor cooling out there, even in humid climate installations.
I think Taco headquarters in RI has chilled beam, and it didn't drip on the high load grand opening event. From what I'm told

Rehau has a dozen case studies on radiant cooling University Chicago N campus, Army Museum, Va, UW Seattle, etc. on their site.

delcrossv

Thanks @hot_rod . I will admit I like the concept for cooling. Still have to figure out how to do air exchanges. Separate ducting or part of an active beam?

I'll bet the administration will want opening windows so cutoffs for dewpoints above setpoint will be a necessity.

Correct me if I'm wrong, but I'll still need a VAV for the gym though. Hydronic HX and blowers, yes?

pecmsg

delcrossv said:

Thanks @hot_rod . I will admit I like the concept for cooling. Still have to figure out how to do air exchanges. Separate ducting or part of an active beam?

I'll bet the administration will want opening windows so cutoffs for dewpoints above setpoint will be a necessity.

Correct me if I'm wrong, but I'll still need a VAV for the gym though. Hydronic HX and blowers, yes?

Are windows allowed to operate?
For security NY schools require fixed windows. Window A/C is being replaced by central systems. Gymnasiums and auditoriums are requiring higher fresh air considerations.

delcrossv

pecmsg said:

delcrossv said:

Thanks @hot_rod . I will admit I like the concept for cooling. Still have to figure out how to do air exchanges. Separate ducting or part of an active beam?

I'll bet the administration will want opening windows so cutoffs for dewpoints above setpoint will be a necessity.

Correct me if I'm wrong, but I'll still need a VAV for the gym though. Hydronic HX and blowers, yes?

Are windows allowed to operate?
For security NY schools require fixed windows. Window A/C is being replaced by central systems. Gymnasiums and auditoriums are requiring higher fresh air considerations.

Private school, so yes, the windows will (most likely) be operable. Everyone wants an open window on a "nice" day. Just gotta figure out how that will work.

pecmsg

delcrossv said:

Thanks @hot_rod . I will admit I like the concept for cooling. Still have to figure out how to do air exchanges. Separate ducting or part of an active beam? I'll bet the administration will want opening windows so cutoffs for dewpoints above setpoint will be a necessity. Correct me if I'm wrong, but I'll still need a VAV for the gym though. Hydronic HX and blowers, yes?

Are windows allowed to operate? For security NY schools require fixed windows. Window A/C is being replaced by central systems. Gymnasiums and auditoriums are requiring higher fresh air considerations.

Private school, so yes, the windows will (most likely) be operable. Everyone wants an open window on a "nice" day. Just gotta figure out how that will work.

Will the building codes allow it?

delcrossv

pecmsg said:

delcrossv said:

pecmsg said:

delcrossv said:

Thanks @hot_rod . I will admit I like the concept for cooling. Still have to figure out how to do air exchanges. Separate ducting or part of an active beam?

I'll bet the administration will want opening windows so cutoffs for dewpoints above setpoint will be a necessity.

Correct me if I'm wrong, but I'll still need a VAV for the gym though. Hydronic HX and blowers, yes?

Are windows allowed to operate?
For security NY schools require fixed windows. Window A/C is being replaced by central systems. Gymnasiums and auditoriums are requiring higher fresh air considerations.

Private school, so yes, the windows will (most likely) be operable. Everyone wants an open window on a "nice" day. Just gotta figure out how that will work.

Will the building codes allow it?

Opening windows? Yes. We're not in NY. Thank Goodness. 😉

pecmsg

Your missing my point. You need an engineer that’s aware of the rules and regulations of the jurisdiction having authority 

delcrossv

pecmsg said:

Your missing my point. You need an engineer that’s aware of the rules and regulations of the jurisdiction having authority 

Sort of getting off topic @pecmsg as I mentioned at the top of this thread that there will be engineering company involvement as the project advances. Not like we're gonna wing it with a multi million dollar project.

We actually do know the local codes here, thanks.

The Steam Whisperer

Steam is still probably the longest life system. High quality power burner steel boilers with replaceable tubes ( for hot water or steam) and modulating burners will get you efficiencies in the upper 80's, which is just a short ways from condensing boilers but without the fuss and 15 to 20 year cycle boiler replacements. If you want you can add condensing stack economizers to get you up into the 90s. You'll probably need to heat your domestic water with these economizers because the water flow rate is so low with returning condensate that can't get that much extra efficiency out of the stack gases.
Probably your best bet for long life boilers is to get rebuilt Pacifics or Kewannees.....we've have lots of them pushing 100 years that have never been rebuilt and we get firing efficiencies in the upper 80's... especially the Pacifics. The exceptionally large combustion chambers with lots of radiant heat transfer surface of these boilers work really well with radiant design burners for uncanny efficiency. With steam you can also eliminate electrical usage for even higher efficiencies or, if you use condensate pumps, you only need at most about 1/160 the hp (yes one one hundred sixtieh) to move water back to boiler versus hot water systems. Designing the radiation with supply orifices generally will allow the system to have return temperatures not much above room temperature most of the year.
Hot water has the inherent problem of freeze up should something go down. And we all know that schools go through long periods of poor maintenance and this is when freeze ups tend to happen.

If you install the system using "minitube" design techniques, your piping system will probably be smaller than a hot water system, saving up front costs too. However, good near boiler piping will eat into some of these savings because steam needs big pipes around the boiler.
A staged boiler heating plant makes sense not matter whether you use steam or hot water, but does require a trully knowledgable designer to properly lay out the piping and sizes of the boilers.

delcrossv

@The Steam Whisperer I agree and it would be a thing of beauty- but that would be an almost impossible sell to the Board /Architect etc. Would be really cool though. 👍

Also steam heat emitters with a bunch of little kids necessitates enclosures. 140 degree CI baseboard , black pipe, with KN mod cons is just an easier sell.

Solid_Fuel_Man

Low mass radiant. Design for the lowest supply water temp as practical. 

You will need some type of air handling for ventilation, so incorporate cooling there. Still can use heat pump in the air handlers. That way it is future proof, with the entire DX system and minimal refrigerant piping which could be changed if the future of C02 refrigerants becomes reality in the next 100 years. 

Just spec welded, soldered, or threaded connections. I've seen way too many large buildings with 3" and up vic piping to save on installation, in 30 years leaks everywhere when the system is allowed to cool. 

One building we have to keep a boiler running year round circulation the main loop so the water stays in!

The Steam Whisperer

If they are really looking for long lasting system and possibly a cheaper up front cost, then it's not such a hard sell. Fin tube baseboard is already enclosed, so no problem there.

Water: Expense of about 2 1/2 times more emitters
Boilers last 15 to 20 years. only single fuel, up to mid 90% efficiency
Possible freeze ups and huge building damage when equipment fails.
About 100 to 150 times more pumping power (electrical usage) needed versus steam

Steam: Much less expensive emitters
80 to 100 year boilers capable of using many fuels up to the low 90% range efficiency
Freeze up very unlikely during equipment failures
Tiny electrical usage

It's not the Pop culture "Green" solution, its a real "green" solution.

The biggest thing they should do is make the building truly efficient, not just on paper. Then the heating system starts being alot less costly.

delcrossv

@The Steam Whisperer I'm fine with floating it, but it'd be essentially teaching the design engineers about a whole "new" type of heating. 😉

delcrossv

@Solid_Fuel_Man Low mass radiant? convectors? Cast BB is high thermal mass, yes? What would be low mass? Runtals?

Cooling seems the easier choice:
Chilled water
VAV boxes w/coils or active chilled beams (Thanks @hot_rod- I'm "warming " to the idea )
DOAS and air handlers probably in a penthouse. Chiller in the machine room. Rejection HX for chiller probably on the roof.

The Steam Whisperer

Probably your best bet for design engineers are good cooling system engineers... they get the importance of phase change and its efficiency benefits. Then get someone like Gerry Gill to work with them on the piping design so you can use the minitube concept or just a down feed system. You could probably go to a simple induced vacuum system which will drop the steam temps noticeably or use a vacuum pump and get steam temps down to 150/ 160F for most of the year. If you have a nice tight system the vacuum pump will only need to run once a day like many of our 80 year old systems. Only a few traps to maintain on the mains with none on the radiation. Modulate the boiler firing capacity on direct outdoor temperature reset with indoor feedback because a well insulated building will need very light heating when filled with lots of people and lights. You'll need an overide control loop to allow the system to move to high output for coming out of weekend/holiday setbacks. A few steam coils and variable speed compression cooling coils to heat'cool outdoor ventilation air with heat recovery ventilators and you should be in good shape. Probably a couple of Ductless splits per classroom for cooling and dehumificiation (stage as needed to maximize dehumidification) will take care of the main cooling load (people).
Using a high mass structure with well insulated exterior skin is typically the best thermal design because the insulation protects the mass from rapid outdoor temperature extremes while the thermal flywheel effect of the mass reduces peak loads on equipment. Your cooling equipment can often be much smaller and teh heating equipment smaller too. Good cooling engineers look at thermal mass and occupancy times as part of design.... I have found that most engineers ignore these design factors and put in way too big equipment. These factors have been part of the design standards for decades but almost always ignored.

The Steam Whisperer

Also, set up the building for passive solar with typically about 30 inch overhangs above windows.... Classroom, offices etc. on South ( and east if needed) and mechanical, storage, etc on north and west.
With good insulation and passive solar heating, the building may be able to stay warm without any supplementary heating when in setback and when fully occuppied on most winter days.

delcrossv

The Steam Whisperer said:

Probably a couple of Ductless splits per classroom for cooling and dehumificiation (stage as needed to maximize dehumidification) will take care of the main cooling load (people).

ASHRAE 62 will necessitate a DOAS, so will the board, especially with "the rona". We put ductless splits as a retrofit in our present building. They work but I'm not gonna recommend them. Chiller+ VAV boxes is probably easiest to hook to a DOAS. Eliminating noise in the classrooms is on my mind, so all the mechanicals should be outside of the classrooms. That's an attraction of active beams, assuming a 2 wheel DOAS can handle dehumidification.

we'll likely need to add humidity in the winter. Transpiration from the kids doesn't cut it based on experience in the present building, but certain rooms do need occasional cold weather cooling.

The Steam Whisperer

If you have a well sealed building, you probably will have to ventilate humidity even in the winter. The ductless splits I've seen were all high end (Carrier and 1970's Sanyos) and wear nearly silent. One installation was in a 1880 stone church with a 1950 slab radiant system, so any noise would be noticeable and it was not an issue.
You'll still need airflow for dehumidfication if you run chilled beams and radiant cooling ceilings.

delcrossv

The Steam Whisperer said:

If you have a well sealed building, you probably will have to ventilate humidity even in the winter. The ductless splits I've seen were all high end (Carrier and 1970's Sanyos) and wear nearly silent. One installation was in a 1880 stone church with a 1950 slab radiant system, so any noise would be noticeable and it was not an issue.
You'll still need airflow for dehumidfication if you run chilled beams and radiant cooling ceilings.

Probably will. We'll need airflow for dehumidification and air exchanges both. I'm looking into if active beams have enough flow to cover air exchange requirements. Something to go over with the engineers when we get to that point.