boiler/chiller setup questions

[brian89gp]

I am finally getting around to finishing the setup of the hydronic system for my house. Hoping some of the experts here can weigh in on their opinions.

Some background info. I have a large/old house, if done the traditional way it would consist of 3 different furnace/aircon units in the 3-4 ton cooling and 70k+ BTU heating each and I would have to have bulkheads everywhere to hide all the duct-work (then add the whole issue of how to hook wood heat into it). It is far easier to have a wood boiler, 200k BTU boiler (backup), and two 5 ton aircon units hooked up to chiller coils driving a hydronic system for the whole house. Overall costs is cheaper too. Planning on using either a Boiler Buddy 119g hydraulic separator / buffer tank or something similar. House is large so it is easy to dump heat or cool ..somewhere.. so storage is not necessary. Its more to act as a small buffer to prevent short cycling the AC units during mild spring/fall days and do double duty as a hydraulic separator between the primary/secondary loops.

The setup:
-5 fan coils (sized for cooling, thus over-sized for heating)
-baseboard radiators near some large groups of windows that are always cold
-radiant flooring mostly used to provide baseline heat (~50% of needed heat load) since it is staple up under existing wood floor.
-in two rooms that are absolutely baked by the sun in the summer, the radiant floor would also have cool water run through to take some of the latent heat load out of the room...when sunny the heat load in these two rooms is about 1.5 tons each.
-the radiant floor would be run through a mixing valve, the other zones are piped direct to the secondary loop
-Delta-T in heating mode is between 15-20* for the fan coils and baseboards
-Delta-T for the radiant floor would vary much more since it is behind a mixing valve
-Delta-T in cooling mode is 10-12*


This setup has one big problem that I am trying to figure out how to solve in the best way possible. Almost the whole system is switched between heating and cooling modes and there is a buffer tank in the middle that will stratify somewhat.
1) If I arrange the piping so the boiler/chiller feed the top of the tank and the secondary pulls water from the top, it works real well for heating but in cooling mode it would put cold source water on top and warmer return water on bottom.
2) If I arrange the piping in reverse, it works well for cooling mode but is backwards for heating.
3) I can put 3-way "L" valves on the secondary side to flip the source/return to the tank. The one big downside is that in order to switch between heating/cooling it would require manually turning two valves. The primary side is easier since the boilers and chillers would have different pumps and they could just be plumbed differently. (the boiler pump could theoretically suck water through the chiller primary circuit, but the resistance because of the pump/check valve/coil would probably reduce it to only very minimal)


One big question I have with rather low Delta-T's and a relatively small tank, is having the tank plumbed for heating mode and cooling being inversed (cold water on top, warmer return on bottom) going to cause much of a problem at all? The tank is not there to store anything, only as a thermal buffer to keep the chillers from short cycling on lower load days (same with the boiler, just to a much less extent)

I know its not the typical boiler question, but appreciative of any thoughts or opinions that anyone may have.


Below are simplified diagrams showing only one boiler/chiller/fan coil/etc. There are check valves after each pump. First one is the simple-piping method that is set up for heating mode. Second one is the one with 3-way valves to 'flip' the secondary side between heating/cooling.

 

[Bob Rohr]

A pair of 3 way zone valves could do that.

Or a 4 way valve, either manually operated or motorized. A Belimo or Honeywell spring return actuator can be adapted to most off the shelf 4 way valves. I think Belimo offers a mounting kit for that.

Some ideas from Idronics 17.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

 

[STIHLY DAN]

How are you going to get rid of condensation on the baseboard and floor in cooling mode?

 

[maple1]

How are you going to get rid of condensation on the baseboard and floor in cooling mode?

Thats what I was wondering about-condensation. But having no experience with chillers, was waiting to see if anybody else mentioned it.

 

[Bob Rohr]

A dewpoint control is used to prevent condensation, often connected to a 3 way mixing valve. In some cases multiple controls are used, additional controls in high humidity areas like kitchens.

Any tank used for storing chilled water needs to be completely sealed and all the related piping. Even a square inch of exposed metal will sweat and cause a wet spot and dripping.

 

[STIHLY DAN]

No disrespect, but if you have a dew point of 70* no matter the control, you will either get condensation or a hot house. If you can valve of the radiant and the baseboard to just use the air handlers with their coils for cooling, that would work. IMHO

 

[brian89gp]

RE: Bob Rohr

Awesome document (the idronics one from Caleffi). I had ran across it before but never scrolled down far enough to see the chiller related things.

I see they are recommending flipping/inverting the buffer tank between seasons so I'll just go that way. The lines from the tank that the 3 or 4 way valve sit on are 2", I've had trouble finding 3 or 4 way valves that large but I'll start calling around and asking. Max flow rate in cooling mode is around 35gpm so I can't really go any smaller then that.

I'm thinking that just having a manual valve would be ideal, the walls are solid brick and uninsulated so there is enough thermal mass in the house that its switched between heating/cooling only once per season. I'll just add a manual heating/cooling mode switch by the valve to lockout the opposing season from running (just in case somebody flips one of the termostats and you have the chiller and boiler fighting each other...)




RE: condensation concerns

The baseboards and 90% of the radiant floor are heating only. The two rooms I plan on running cooled water through are special cases where its almost impossible to make the room comfortable any other way, I'm not planning on using the floor to actually cool the room just take the excessive latent heat out of the floor. The two rooms have one wall that is a giant bay window, 36 sq/ft of glass facing SE, 36 sq/ft facing south, 36 sq/ft facing SW, no shading and a concrete driveway and a shorter houses' roof next door that the sun bounces off of and through my windows. The wood floor will heat up to 100-110* or higher every day because of the sun, when the AC is running the room is tolerable but as soon as the AC turns off the room 'feels' very hot due to the wood floor being so warm. I love the bright sunny room, I really dislike how intolerable the room feels with the swings in temperatures.

I am hoping to run 60-70* water through the floor to take some of the latent heat out of it directly vs trying to cool it off by freezing the room with air-blown AC. A mixing valve would keep the temp at or above the 60-70* mark. The warmer temp is above the dew point generally, but I was looking into a dewpoint controller as extra insurance against condensation. These two rooms radiant floors' would be on a different zone in heating anyway since the sun can easily heat the entire room on a sunny day in winter.

How to do this...I'm not yet sure. I'm guessing the Caleffi document holds a lot of info about it though.





Design specs for the chiller coil are 54* entering water tem and 44* exit water temp with a 34* evaporator condensing temp (Douchette CC500 coils). The air coils are sized to run on the same 10* delta-t in cooling mode (Magic Aire 3 and 4 ton coils).

As a nice side benefit of having the air coils sized for low delta-t cooling, the are oversized for heating. They provide enough heat with 120* water.


Putting the hydronic system in the middle of the heat/cool source and the coils for the house actually have a lot of benefits. Don't need bypass dampers and more expensive variable speed sensing furnaces to prevent the furnace burners from overheating, or the same concerns to prevent the AC evaporator coil from freezing over. Or simplifying. 2 AC condensers vs 5. Or one larger gas boiler and a wood fired boiler, vs 5 different gas furnaces and somehow working wood burning heat into it, such as a wood burning furnace heating only the first floor and letting it convect up to the rest of the house. Front stairs from street to house are a 15' vertical rise flight of concrete stairs that are old and need to be replaced. would love to put in hydronic snow melting tubing when I have them replaced so I don't go through 10 gallons of snow melt every year keeping them free of ice.

 

[Bob Rohr]

ceiling convectors or chilled beams are another common method for radiant cooling. The new Taco training facility in RI has a chilled beam system in a fairly high humidity area.

This product is made in Buffalo NY and I have seen it on a number of projects. No doubt a handy DIYer could build something unique along these lines.

I like to stay away from forced convector systems due to noise, one of my pet peeves although ECM and variable speed blowers soften the volume somewhat.

 

[brian89gp]

ceiling convectors or chilled beams are another common method for radiant cooling. The new Taco training facility in RI has a chilled beam system in a fairly high humidity area.

This product is made in Buffalo NY and I have seen it on a number of projects. No doubt a handy DIYer could build something unique along these lines.

I like to stay away from forced convector systems due to noise, one of my pet peeves although ECM and variable speed blowers soften the volume somewhat.

Zone dampers with over-sized duct work help too. I don't like the sound of a forced air system running all that much either.

I'll have to do some research into the chilled beam systems. I've done some reading about chilled panel ceilings and whatnot but the amount of metal they require is rather cost prohibitive and harder to accomplish in a home without having an industrial/commercial look to it. That would be awesome though having the chilled beam running on warmer supply temperatures doing most of the cooling for the house and just using the forced air coils for the extra capacity during the super hot days or for quick recovery purposes. I am only interested in the passive systems, the induced active systems would be a lot harder to DIY.

 

[brian89gp]

Decided to use an electric water heater using the 1" taps as an inline buffer tank sitting before the chiller coil. No need to deal with inverting the buffer tank between seasons this way and since the buffer is only meant as a means to guarantee a minimum runtime and not as thermal storage, this way works just fine. Lot cheaper too.

Rob Rohr, read up a lot about chilled beams. I like the idea a lot of radiant cooling but think the chilled beam is just a little further then I want to go. Instead I am pretty sure I am going to do a radiant ceiling instead, keep the water above the dew point. Armchair calculations say it should handle a decent amount of cooling load for the house, and I have 10' ceilings so the air stratification and temperature delta in the room is usually pretty large. I'll keep the forced air coils for rapid recovery (both heating and cooling) and also for de-humidification purposes. Oversize the ductwork and run the blower fan on a super low speed for dehumidification and there shouldn't be much noise of blown air since the velocity would be low.

The rooms with a lot of glazing I'll run chilled water (but above dewpoint) through the floors, and put radiant panels under the three locations with a large group of windows to help with the bad draft off the glass that occurs in the winter time.

 

[brian89gp]

Flow checks and shutoff valves not shown.


Air coils require 7.2-9.6GPM on the 4 ton and 4.8-7.2GPM on the 3 ton cols, each. Really want to use a Delta-T pump on these, possibly one larger pump with zone valves or even individual pumps for each zone. Just having trouble finding pumps that would operate in both chiller/boiler modes with two different setpoints without needing to reprogram the pump twice or more per year.

For the chiller, wanting to use a circulator such as the Taco VT2218, it has options to decrease speed on temp rise (set point heating, measuring the chiller coil output side) to try and maintain a 44* chiller setpoint, or possibly running it in Delta-T mode

There would be a very large amount of radiant loops, ceiling/floor in each room on their own loops. 2+ looks combined onto the same zone valve. Going to run a large 2" manifold down the center of the house about 30 feet long and hang all the zone valves off of it to help reduce loop length and head loss. Planning to use the Taco VR3452 running in set-pressure mode. If all zones call I am expecting somewhere around 40GPM of flow

All of the radiant loops will be ran through a large 3 way motorized mixing valve (unsure if it will be 1.5" or 2" yet). Still looking for a suitable controller for it.