heating large buildings

cgutha

A few years ago, when our local hospital was building new, the subject of how to heat the new building came up. I seem to remember mention of a European system where four pipes ran through the hallway of a wing, then each room (or zone) would tap off these to feed a two-pipe radiator in each room. The two-pipe mixture of each room would receive a variable temperature so that a constant fan would satisfy the heating or cooling needs. Does anyone know anything about this? I have forgotten what it is called.

hot_rod

A four pipe system provides both heated and chilled fluid to various emitters

There are conditions where heat and cooling is need in different areas at the same time

with a two pipe system you have to make the switch at some point to one or the other

cgutha

Thank you Hot_Rod, the control valve takes either the heat or chilled water as needed. sending the fluid to a single coil. Therefore, the fluids in the boiler and chiller must be the same glycol (assumed) mix. The return line must be controlled also so that the volume used from one or the other is returned at the same rate. I imagine that the valve would be something like a two-way hydraulic valve. where the bucket or whatever is controlled with accuracy. only here we are controlling the fluid temperature to the coil.

hot_rod

Here are a couple examples of piping.

On fan coils there is usually a "coil kit" this includes the on/ off valve, balance valve, strainer, bypass, etc.
Here is a 149 coil kit Caleffi offers

You could also have a mixing valve at the coil, thermostatic or motorized. That could be controlled by a room control or BAC automation control.

Belimo has a valve called the Energy valve that is a control and mixing valve in one package.

cgutha

Yes. figure 5-7a is what I am talking about. who manufactures, supplies these systems?

EBEBRATT-Ed

It's common with large building to have to heat the exterior zones and cool the interior zones at the same time.

Back in the 80s a common system used heat pumps with a boiler and a closed-circuit cooler (similar to a water tower. That system seemed to fall out of favor but was very popular for a while.

Some systems use a 4 pipe system 2 hot and 2 cold pipes with separate chilled water and hot water coils in the air handlers.

there are many different ways to accomplish this.

Is this a new building or a retrofit??

GroundUp

Pretty much all healthcare facilities are that way. I installed several dozen of these systems around the MN metro area

cgutha

This is a retrofit. The old heat plant is beyond its life expectancy, it needs removed and replaced.
The chillers appear to be ok for now.

cgutha

I see the picture above uses a heat recovery chiller. This is silly. in the summer extreme I need 100% cooling, what do I do with the excess heat? and in the six months of winter... no matter. a separate boiler and chiller will do better. the heat pumps of the 80's fell out of favor because after twenty years they fail. now, they must be removed and repaired. no heat pumps for me.
even having so many valves is future work. but i will place them in the hallway where they will be accessible via dropped ceilings.
Thanks everyone for your responses.
I still have many questions. the control for the valves, and the t-stats for example. where do I find these and which system is best?
on the other end, the temperature control for the heat and cooling loop. Do I use a variable speed pump to maintain pressure when there is no call on one of the legs? lowering the boiler temperature in summer is easy, but the chiller is not so forgivable. this may require a threeway valve to deliver temperatures that vary.

bburd

This kind of thing in large buildings is not an in-house job. You need an HVAC engineer or commercial design/build contractor. 

hot_rod

The local climate may dictate how you design the system, certainly on the cooling side

Some cooling options here
https://www.caleffi.com/sites/default/files/file/idronics_28_na.pdf

The Belimo energy valves maintain a delta t which helps efficiency and performance if the cooling system

Its worth watching a video to see how they work and save operating costs.

 Variable speed pumping properly applied increases comfort, reduces pumping cost, and can extend service life by eliminating overpumping during low load conditions

cgutha

Thanks Hot_Rod. yes, this will take an engineer and contractor. I am simply doing preliminary work, so we have an idea of what I am looking at. I have crunched some numbers in order to get a budget guess. but I need to know the control systems are out there. without making things too complicated, (I know there are building programs such as Johnson controls) but having a computer run a building is great until the program becomes obsolete or the computer crashes. so, I am looking at simplifying where we can while improving comfort and reliability. Computers and electronics have a short life span. what I buy today is obsolete before it is installed -- especially when it comes to the fire detection system which I am not talking about. but the same thing happens in heating systems. Johnson control puts in an air system that requires their parts. now when a t-stat goes out it is $100 to replace it. and the diaphragms eventually go bad. or water gets into the system. Efficiency means more than fuel costs. I need to know the life expectancy and the cost to maintain everything.
I have worked in buildings with nearly every kind of systems. all at the end of their life.
Thank you all for your input. i ask you questions because you know more than me and I need to learn. I heard about this system. it sounds as if it has possibilities. I look for simplicity, ease of repair and cost effectiveness. Thanks for putting up with me

hot_rod

Most all controls are able to be used as a manual, electronic, or digitally controlled 

wifi enabled is becoming more common also. So options from mild to wild for controls

EBEBRATT-Ed

No matter what modern control system you put in they are all proprietary now. Your pretty much stuck with the manufacturer you install as far as the controls go.

The valves and damper actuators are a different story, you can install any brand you want.

In the old days with pneumatic controls, you could mix and match parts from different manufacturers if you wanted to and the system would work.

cgutha

wow. I asked about a system I had heard of wanting to know If I had heard correctly. In twenty-four hours not only has this been confirmed but I have leads on contractors and suppliers. I thank you gentlemen. Now, I can take this information to my team and wait for them to catch up. It looks as if it will cost twice as much as I had hoped, but right now, everything does. I see that the PEX expander I bought three years ago is worth three times the money. thanks again. Now, I wait. I will let you know when we are ready to take bids.

cgutha

There is one more thing. This might take a computer program. In the summer, the demand for heat is zero. all the valves are asking for cooling. The variable speed on the heating supply pump slows down. At the end of the supply line, I want a half inch circulating pipe connecting to the return line. Much like the domestic hot water return line. Let's say that the pump is set to maintain 60 psi working pressure. When all the valves are closed the pressure increases, the pump slows down, but the pressure increases to 65 psi. I want the boiler temperature to decrease by a few degrees (with a limit of 80 degrees.) In the winter, when all the valves are open, the pump runs at maximum, but the pressure drops to say 55, the water temperature increases with its limit of 190 degrees. so, the pumps are variable speed, and the temperature also is controlled by the pipe pressure. In the winter, the opposite is true for the chiller. the range is from 36 to 60 degrees. depending on the demand as indicated by the pressure. Does anyone do this?

RPK

Variable speed hot water and chilled water distribution pumps similar to what you’ve described are very common in commercial buildings. Keep in mind that pump speed would be controlled based on differential pressure between supply and return lines. Differential pressure is typically measured/monitored for this purpose at a remote location or sometimes multiple remote locations. Often, minimum flow bypass is provided via a modulating control valve. As control valves at terminal units close, the pump slows down, once the pump has slowed to min speed, if the differential pressure continues to increase, the bypass valve is modulated open. When demand begins to increase again and differential pressure begins to drop off, the bypass valve is modulated closed to increase differential pressure. The pump speed is only increased above minimum once the valve is fully closed.

Resetting hot or chilled water temperature based on outdoor air temperature is standard practice. I have never seen the reset function tied to differential pressure control and am not sure I see any potential benefit in doing this. In the example given, it sounds like you are using pressure and an indicator of heating or cooling demand. In a properly functioning distribution system as described in the paragraph above , differential pressure would not be a good indicator of demand.

cgutha

It could be that I do not understand fully how the system works. My idea of controlling the medium temperature via the pressure rather than ambient temperature is that the pressure should be an indicator of the actual building demand. again, north side with wind, vs south side with sun. each room has a different demand. as the valves close the pressure increases, the pump slows but the temperature also changes. the valves may reopen because the Delta T has changed. The pump may return to a faster speed because the building is satisfied with the new Delta T.
I hope this gives a better indicator of the instantaneous heating / cooling demand of the building room by room, zone by zone.
In either case, I hope I have enough specs to give to the bid writers.
thanks.
I still have to take this to the engineers / contractors.

cgutha

RPK, Differential pressures. I know they exist; I do not know the detail. I have never worked with them except to monitor the speeds and make certain they are working.
Let's say that the differential between supply and return is 10 psi, at 5 psi, I can slowly control the temperature. the valves react accordingly, at 8 psi differential, I can change the setpoint at a faster rate.
Will it work? maybe, maybe not. I can always go back to the ambient temperature.
i know the buildings "flywheel effect" gives a delay to the actual load.

hot_rod

It is much much easier to control heat output by changing supply temperature, it is a fairly linear correlation 

Try to adjust output by changing flow rate or pressure is not as easy of a task. With delta P circs you will not see a lot of pressure change. 

In fact most ECM pumps with delta P function have a constant pressure setting.The pump control function you select has a lot to do with the piping method.

This is why indoor and outdoor reset is so common. Most heating equipment has outdoor reset function built in now. Possibly chillers and heat pumps also

Indoor reset could be a function of the room thermostats

Read up on the néw circulator logic and how to apply in Idronics 16

EBEBRATT-Ed

It is common to control pump speed with a variable speed drive wired to the pump motor. The vfd is wired to pressure differential sensors. Although the sensors are sometimes installed near the pumps for ease of installation they should be 2/3 of the way down the length of the main for best operation.

Kele Associates in TN has those types of pressure differential sensors.

Many installations now use 2 way valves where 3 way valves used to be used. 3 ways were used before VFDs became available and provide pumping energy reduction when the pump slows down.

The best way I have found is to use two way valves on the ahus except a few ahus on the far ends of the mains. You should install enough 3 ways to provide enough flow for the pumps minimum requirements.

Or you can use a pressure operated bypass valve.

hot_rod

The new ECM circulators have a lot of control logic built into them. It should be able to accuratly control most any system to the highest efficiency without any external controls.
Typically these type circs are powered 24/ 7 and they ramp up as the onboard pressure sensor determines a need to provide flow. There is no need to even have. "call" for flow to thses pumps.

If this is to be an engineered design, engineers tend to have "favorite" piping systems that they use over and over.

PSC motors on circs over 1 hp have been banned so you pretty much end up with ECM technology in larger systems.

2025 is allegedly the date when all circs will be required to be ECM, according to a recent Taco webinar.

These graphics show how the different pressure modes are used.

And the boiler and chiller would still modulate temperature.

cgutha

Using the ambient temperature to determine the heating and cooling set point is Tried and true. Keep it Simple. Why mess with what works? Okey.
I am trying to remember. there were times when we had to go in and manually change setpoints to kick start the heating or cooling.
When the outside temperature would swing thirty degrees from morning to evening, things work well. however, on cloudy days where the temperature would hover at sixty to sixty-five degrees for a week, I think this was where it failed.
But then, the system described above is not what we had.
we had heating coils and Remington through the wall units in part of the building. Remingtons do not work when the heat is on.
Hence the change to a true four / two pipe system.
Under these conditions, a heat recovery chiller would be useful. The large chiller we had did not like to run with a small load.
Again, if we were heating at night, Then in the morning when we needed to cool, the units would still be hot, now there was no cooling. the night shift had to anticipate the weather and manually turn the heating off so it would cool before morning.

hot_rod

The current equipment does a much better job of responding to changes in loads in katge buildings

Any building that see large swings in occupancy is challenging to control and keep comfortable

Churches and schools go from empty spaces to full occupancy in minutes. And every person in those spaces could have a different comfort range as far as comfortable temperature

In addition you need air changes and that air needs to be conditioned 

with todays modulation pumps and equipment can better respond. Controls can learn usage patterns and even predict when to start responding. Some thermostats gather data on incoming weather and  start responding in anticipation, to eliminate lag time

retiredguy

If you are looking for a good engineering firm to take care of your heating and cooling projects I would call the H F Lenz company in Johnstown, Pa. At 814-269-9300. They have been in business for about 75 years. I have no interest in this company but know that they were one of the best engineering companies. If they are not in your area they will probably recommend someone that can fulfill your needs.

cgutha

thanks