Hydronic System

[NewbeeMC9]

I have not seen any post about the Hydronic systems being used as chill water for A/C.

Is any body doing this?

We used chill water in the navy to distribute Cooling (or heat removal whatever you want to call it)

Just seems you could use the same system in the summer that your carrying around anyway.

[Chaz]

Really.......... I am not familiar with such a system. How would it work??
I did 4 years in "Uncle Sugar"s Canoe Club", but I was a crab. (Seal Beach Naval Weapons Station) Since I don't have enough salt on me to salt a bag of fries, I can't say as I have ever come across a system like that but I am all ears............ er....... eyes.... as the case may be. 
  How does it work?? Please enlighten.
       Chaz

[makemineatwostroke]

NewbeeMC9, you need refrigerant and a compressor to chill the water

[Stan]

The system is very common in large buildings. Just circulate air over hot coils in cold weather and cold coils in hot weather. I never heard of it being used in a bus. For the people with engine overheating they could use it to cool the engine coolant, just the reverse of using a Webasto (or similar) to heat the coolant. The basic system would have a refrigerant unit in parallel with the heating boiler.

[NewbeeMC9]

Yep Chaz,

AC ran all the time,  distributed by chill water and coils w/fans all around to cool the air.  Basically like what Stan and MMTS said.

I believe Homegrowndiesel was using an automotive compressor off the genny motor but i don't know how he distributed the cool side.


It just seems like you wouldn't need two systems and one be dormant when the other is in use.  When they kinda do the same job.  Maybe just part of it could be dormant.


I hadn't heard of anybody doing it in a bus either Stan,  but would it be a difficult idea?  Maybe somebody has tried it.


Just kinda wondering

[gumpy]

Isn't that what a heat pump does? 

I know some that have installed basement air systems with heat pumps built in. They don't work well below about 40 degrees.

The first problem with trying to use the hydronic system for cooling is you have to first isolate it from the heater, since generally, the heater is used to produce domestic hot water, too, so it needs to be heating during the hot weather, also. The second problem
is that even if you figure out how to soak up the heat inside the coach with the coolant, you then have to remove the heat from
it, so it can be recirculated back into the coach to soak up more. That requires a refrigerant type system, which brings you back to
two separate systems.

[Lin]

Using chill water systems, as mentioned, is common in commercial buildings.  You have a chiller that cools that water to somewhere around 50-55 degrees.  This water is pumped to what they generally call air handling units that circulate the water through a coil and blow air through it.  The heat in the air is picked up by the water.  The air is thus cooled, while the warmed water goes back to the chiller.  It works the same way as the hydronic heat systems that some use.  The idea is that it is easier to plumb, and daisy chain, water lines in large applications than it is to plumb refrigerant lines everywhere.  Actually, the building will use the same system for heat.  One problem using it for cooling that you do not have with heat is the condensate.  As the air is cooled, the humidity condenses on the coil, drips down and must be plumbed to a drain of some sort.  This is true if you are using a split system with your compressor and condenser in one location and the fan-coil mounted elsewhere.  It could be done in a bus, but I am not sure it is worth the effort.  The space is small enough just to blow or duct the cooled air anywhere you want it or plumb the refrigerant if you prefer a split system.  However it is a first class system.  You could even do what used to be called a reheat system which was once common in the days of cheap energy.  They used two coils.  One cooled the air below what you wanted and then the second coil heated it a bit to get to the delivery temp that you required.  This way the humidity was striped out too.

It has been a while since I dealt with this stuff seriously, but I think I still have the basics right.

[TomC]

While it is possible to set up a chilled water system utilizing the heat exchangers used in hydronic heating, a chilled water air conditioning system is both expensive and bulky compared to a roof air conditioner.  Besides, anytime you convert one medium to another then to another- like the mechanical energy of the air conditioning compressor to compress the freon, then the expanded frigid freon cools water, which goes through pipes, then the goes through the heat exchanger to cool air- you loose efficiency.  There is nothing more efficient than applying mechanical force directly on what you want done.  That's why roof airs work so well- mechanical energy of the air conditioning compressor compressing the freon, then the expanded frigid freon directly cools the air through the coils-see the difference?
This is also why you don't see steam powered trains or steam powered commercial ships-they burn roughly twice the fuel to obtain the same horsepower that a direct reaction engine (mainly a Diesel engine) would get.  Good Luck, TomC

[Bob Belter]

Ahoy, Bus Converters,
My Eagle -01 HAS an installed hydronic heat/cool system.  It is remarkably effective  --  but with one serious fault!!!

Condensation on the cold hoses in the baggage bays and up in the bus.

I wrote an article on this subject which was published in Bus Conversions magazine a few months ago.  From your comments, I don't believe that you guys are reading the magazine.  Read it.  My hydronic system is not philosophy or conjecture.  It is completed work.

Enjoy  /s/  Bob

[Lin]

Bob,

I should have mentioned in my last post what you obviously know that another issue with chill water cooling is that the pipes much be well insulated.

[Tim Strommen]

As a counterpoint to TomC's comment:

...Besides, anytime you convert one medium to another then to another- like the mechanical energy of the air conditioning compressor to compress the freon, then the expanded frigid freon cools water, which goes through pipes, then the goes through the heat exchanger to cool air- you loose efficiency.  There is nothing more efficient than applying mechanical force directly on what you want done. That's why roof airs work so well- mechanical energy of the air conditioning compressor compressing the freon, then the expanded frigid freon directly cools the air through the coils-see the difference?...

A roof air must be run at the time of heating/cooling need.  A style of hydronic HVAC&R which is quickly gaining favor in commercial and high-end residential systems is running the high-energy demand cooling system when the energy is cheapest (i.e. at night) - and I'm sure many have had the experience of a campground where everyone and their mother was running one or two 30Amp roof-airs during the day causing the whole site to have a power sag (or blown breakers).

With a hydronic cooling system, you can have an automotive A/C compressor on the prime-mover while you are driving, and/or one on a genset, and/or you can run a DC house-battery powered A/C compressor or line-voltage A/C compressor at night while the energy usage is low and run the refrigerant into an insulated water tank which is making ICE.  This is a "phase change", which has the ability to store an awful lot of BTU absorbing potential energy - and it's the same principal which the mechanical A/C system uses (only instead of a liquid to a solid - refrigeration systems do a gas "vapor" to a liquid).  Ice creation is the same principal used in marine "holding-plate" refrigeration systems, where a A/C compressor is used for a short time to freeze a brine solution in a metal case within the refrigerator or freezer box, then as the ice melts it absorbs the BTU's from the space around the ice case.  Once you have the ice, you switch some valves from heating to cooling and circulate the hydronic system's fluid through the ice block to pull BTUs from the air-to-water exchanger down into the ice block (thus melting it as it absorbs heat).

If you already have a hydronic system installed, it's not too much more work to add the necessary valves to both heat and cool a water-to-air heat exchanger.  But as others have mentioned - one must now account for moisture in the air.  It does allow for a more complicated yet more efficient over-all system even getting into the commercial type Variable-Air-Volume (VAV) high-efficiency HVAC&R systems.


If you are heating water and storing it hot (not just domestic "potable" water), you can pull in heat from several places:

• Water-to-water loop to the prime mover.
• Water-to-water loop to a water-cooled generator.
• Water-to-air loop to the generator's exhaust.
• DC house-battery or AC line-powered direct-to-water heating elements.

This basically works the same way as most of the hydronic systems already discussed - only with the exception that you can transfer back the BTU energy stored in the hot water tank to the prime mover or generator to warm it up before a start.  The biggest draw-backs as TomC had stated is the complexity and space a system like this takes.  To prevent freezing of the hydronic water circuits, the fluid used must have some antifreeze in it which prevents an installer from directly attaching it to a fresh-water system.  In the idealized installation, one would have a tank of fresh-water (100+ gallons), a tank of hot fresh-water (potable water, in a water heater?), a tank for the creation and storage of ice (brine solution - not potable), and a tank for "boiler" hot water.  Without considering the black and grey water tanks one would have - this is a lot of space for a bus to dedicate to water, and in order to keep the vehicle stable it would have to be mounted low (so it would take up a bay or two).  Not saying it can't be done (in fact it could and may be practical for some), but a serious question of "should it be done" should be asked...



Another place one might be able to save energy (more practical - especially if you intake external air to keep the air quality up) is an air-to-air heat exchanger.  A device like this simply attempts to equalize the temperature difference between the incomming air and the outgoing air.  On a cold day, the incoming air is warmed by the warm outgoing air - while on a hot day the warm incoming air is cooled by the cool outgoing air.  This makes the load on the the heating/cooling system a bit lower since the air system is recovering some of the BTU energy it put into the air mass which it is blowing out of the controlled environment into the fresh air it is pulling in.

Cheers!

-Tim

[kyle4501]

Another aspect is that this system will allow shorter runs of the high pressure freon lines. A leak in the chilled water line would be easier to fix    & keep the A/C working.

You could also use multiple refrigerant compressors:
one on engine
one on genset
a small elec that could run off minimal power supply
a large elec that can be used when sufficient power is available
(If one compressor 'went to lunch' you'd still have options for keeping cool while scheduling the repair.

The energy storage tank has the benefit of A/C with minimal peak power draw - AND you can chill the tank while driving & enjoy A\C all night while boondocking without having to run the generator.

The size of the cold storage tank will be the trick . . .
Fast rough numbers (with assumptions to make the math easy  )
100 gal of ice will take ~120,000 BTU to melt.
Which is ~4 hours of 30,000 BTU/hr cooling

Hmmmm, my roof air cycles at night, more time off than on, so this has some practical possibilities, if you're up to the uniqueness of the system.

If I remember correctly, HomegrownDiesel is doing something in his freezer with a 'eutectic' plate to help minimize the fridge's power consumption. . . . maybe Bill can chime in with his thoughts

[Jerry Liebler]

Several facts conspire to make 'chilled water' cooling with the same heat exchangers used for heating difficult.  Let's use an example of one of the 'toe kick' heaters in my bus.  It is rated at 7,000 BTU/h in heating.  This rating is with 180 degree water heating 70 degree room air (we note a 110 degree difference). When we try to use it for cooling  about the coldest we'd expect the water to be would be, say 40 degrees (the temperature difference is only 30 degrees).  Well, it looks like we've only got a little more than 1/4 the temperature difference and that's going to cause about the same ratio of heat exchange capacity.  Of course we can overcome this by installing FOUR TIMES the heat exchange capacity. 
   Another fact  heating can achieve much greater temperature differences per BTU than air conditioning generally can because of the energy needed to remove the moisture in air.  Often half of the cooling capacity of an air conditioner is being used to remove water, called 'latent heat' leaving only the remainder to lower temperature, called removing 'sensible heat'   The other fact is the only water chilling systems available have huge capacity.  It might be possible, however, to use a heat pump intended to cool and heat a swimming pool in a bus.  I'll leave these experiments to someone else.
   I'm convinced residential ductless minisplit heat pumps are the most cost and energy efficient cooling and heating units available for bus conversions.  Roof tops are simply rated dishonestly.
Regards
Jerry 4107 1120

[Jerry Liebler]

Craig,
    You said:  "I know some that have installed basement air systems with heat pumps built in. They don't work well below about 40 degrees. "
    Not to be 'Clintonesque' but it all depends on how you define "well".   
I have a heat pump in my house, with resistance heat back up, and it has easily heated the house, without the backup, even when the outside temperatures were 0 degrees F.  I also have a heat pump in the bus but it isn't big enough to be the sole source of heat yet it has, maintained the interior at 55 when the outside temperature was 20 overnight.  According to the maker of the unit in my bus it will provide 15,000 BTU/h of heat in 0 degree outside temperatures.  Key to a heat pump working in temperatures below 40 is a defrost cycle.  Most of the 'roof warts' sold as heat pumps, and possibly the RV basement units as well, do NOT include a defrost cycle and simply shut down if it gets to where it is needed.  Buyer BEWARE.,
Regards
Jerry 4107 1120     

[Nick Badame Refrig/ACC]

Hi Guy's,

Heat Pumps heat very well down to 5 to 10 deg.  until there is excessive moisture in the outside air. [humidity]

With excessive humidity, the evaporator [outside coil in heat mode] will frost up sending the system into defrost and

bringing the electric back up elements on inside to compansate for the loss in heat transfur. This defrost cycle is a major inefficency

in the system because the defrost cycle is basicly the system switching back to air conditioning and chilling the indoor coil with

cold freon. The electric elements at this point are fighting the chilled coil and also trying to maintain heat out the vents.

Hope this helps
Nick-