Because your profile states you are a contractor, I moved your thread to the “Tech to Tech Chat - Commercial” forum. The AOP-Commercial forum is where equipment owners can ask non technical questions.

Please take note of this new location as the "Moved" icon in the other forum will only last a day.

 

Yes. Latent capacity & control may be issues.

 

the heating coils may have been reheat coils to help with dehumidification.

assuming the coils you are referring to were hydronic coils, could pump cold water through. if refrigerant
coils, would not work.

if downstream of existing cooling coils, if the air off a/c coils is 55-50 degrees, then 50-55 degree water through a second coil won't add any cooling.

 

Laser therometer at 3 different air vents show 65, 65, 67.5, I think the chilled water may be at like 45 degrees. These air vents have air traveling a bit to get there so I would assume its a little cooler at the point the cold air is created and heats up along the way. I do believe there is room to cool this air down but perhaps the air is moving too fast to have is properly cooled and would benefit from the additional contact.

 

Will the existing cooling systems maintain a 50% RH in the conditioned spaces?

If so; the existing heating coils could be used for sensible cooling by maintaining their temperature just above the dew point. To do any latent cooling with heating coils would require that the heating coils have condensate-catching drain pans installed under them.

Heating coils are made differently than cooling coils as the temperature difference across heating coils is greater. Heating coils operate at over 100º difference to conditioned space. Cooling coils operate at about 30º difference to the conditioned space.

PHM
--------

Hello

I would like now know if its possible to pipe in chilled water into the heating coils in the air handler be used as cooling?

A little background infomration, I have a commercial water chilled unit in a very hot and humid part of the country which is basically summer all year round. I think most of the HVAC equipment is original from the 60's except for the water chillers which are relatively modern.

For some strange reason, the original builders put in a lot of heating equipment that never gets used. In fact, I have had to tear out a lot of the healing equipment just to make room for my other more important things.

The HVAC is unable to keep as cold as I would like yet its not a problem with the tonage as the water chillers will periodly turn off then turn back on again when needed. I think its unable to convert all that chilled water into approperate cold air.

One of the ideas I had was to use the heating coils in the air handler as cooling coils by having chilled water run though them.

Again, I don't care at all about heating as I have scrapped heating equipment for space already. I just need to get things cooler by whatever means necessary.

Can the heating coils in the air handler be used as cooling, if chilled water was piped into them ?

Thanks.

 

Nobody is concerned about the heating coils not having condensate pans underneath them?

 

Details, Details!

 

I would first thoroughly investigate the whole chilled water system. A system 60 years old and unable to satisfy the spaces has a problem somewhere, and it is unlikely to be a design issue (have they been unhappy all these years?). I would not be surprised to find that the problem began sometime before the new chillers were installed, and that it was thought that would fix everything. It is not unusual to find a control system that old to be "jumped out" in several areas.

 

Original system had around 15 tons, new chillers have 20 tons. Inside equipment was design for 15 tons. Outside units turn off becaused chilled water too cold while inside still too hot. Being able to drop a few degrees would make a big difference.

Recently chilled water pipes under the house was found to be missing insulation in a few different places but that has been fixed. More insulation added to attict and ventalitating fan removing out 100+ degree air during hottest part of the day.

All effort has been going into cooling things down, the more the better. Even during winter when its somewhat cold outside for this area, just turn the AC off and its warm inside. Maybe it's the servers inside or the stone absorbing the sun, etc... Whatever the reason. Even without a heater in winter, still gets warm inside.

AC usually running in winter and if it ever gets too cold, just turn off AC and its warm inside. So no option is off the table to get things cooler.

 

Or fouled coils…

 

Excellent point! And if the air side of the either the heating or cooling coils are dirty then the airflow through both will be affected.

 

Outside of there is no condensate pan as several have mentioned. The heating coil is not as big as a cooling coil. You would never get the performance.

Now if you just used a coil dedicated for heating, but was big enough to give you the BTU you needed then it would work. As long as everything else was in play.

 

Just need a little extra cooling would do it. A few degrees colder would make a world of difference.

 

unless its 85 in building, 65 sounds like too high temp for supply. either duct issues or the ac isn't working well, as others said.

 

In other areas where there is an air handeler above the room, the temperature is much cooler. Something like 56 degrees.

The common area has all the cold air supplied from a central air handler and the air has to travel a bit before reaching the destination. Sometimes comes out hotter than 65 degrees. This is the one that we are considering using chilled water in the heating coils to get some cooling.

This supplies air to many large rooms. Air entering this central air handler goes so fast that perhaps it does not have enough contact time to get properly cold or the older system did not work at well as modern ones.

I was recently at a hotel where the room would not cool. I could not sleep and started sweating in the heat. The next day, I called and they sent an a someone who could not fix it and eventually there was an entire team. After all was said and done, they could only get like 65 out and the guy said it had chilled water at like in the 40's. So I don't know if this is hotel software overriding all the equipment to save power.
Even the 65 was a vast improvement over what the temp was the prior day. I could finally get some sleep.

Difference is that the hotel room was very small and in the building, the rooms a very large and 65 degrees(sometimes hotter) is not cutting it.

The coils are clean so that is not the problem. Are you suggesting the vent may be leaking?

 

You are dragging a dead cow around. I'm betting just the refrigerant type will sink the cost of any modifications - or the conversion of such. Maybe the air handler might be able to be reused but you need a properly sized matching DX system inside of that existing cabinet if your are going to have any kind of change and are on a limited budget.

 

Chill water system

 

Is there any way to slow the down the water through the air handlers? And maybe the water at the chiller?

When I first found this forum I told of a chilled water system that was no longer cooling. I did fix it, but did not understand the dynamics of why it ended up working so well. Let me give a bit of background.

The room was probably first built as a server room. Can't remember too many details. Chiller was maybe 20-30 tons (that part really doesn't matter). To the best of my memory, there were 3 air handlers. The room had gone through a couple of re-use 'applications', and the cooling just didn't work any more. Occupants of the building kept requesting bigger and larger equipment, even though HVAC engineers said there was plenty of capacity.

Now enter me. One problem, if I remember correctly, the room was empty, waiting for the next use, so no heat load for me to work with. Maybe I turned off the chiller to allow heat to build up overnight. I didn't know a lot, but I knew some basics, just some stuff normally used for troubleshooting. Let me cut to the chase.

When I turned the chiller back on, at 'full load' I only had 3*F temp drop across the chiller barrel, and even though after the chilled water met set point at the chiller, also had very low temp drop at the air handlers.

I was able to get the original engineering drawings. I went back to measure the water flow. Found the gallons per minute way over the top. Measured both at the chiller and to confirm, measured the air handlers as well. Found all circuit setters opened 100%. Can't remember the exact order I made the adjustments, probably the chiller first, set at or close to what the engineering drawings called for. Then adjust the circuit setters at each air handler.

Now we have cooling! Even those who spent years or decades in the building could tell (with no heat load) that things were working better than they could believe.

I had my 10*F drop across the chiller, and the air handlers were putting out cold air. But I really had no clue why. And, obviously, in the years/decades previous, the other techs had no clue either.

The only thing I could fathom is that the water was staying in the chiller barrel longer to get colder, and staying longer in the air handler coils to pick up more heat. But in my head, even that was still difficult to fathom.

Shortly after I joined this forum I posted this service call. I had people telling me I was nuts, all sorts of crazy disbelievers. Until someone came along who understood the dynamics of what I fixed. Keep in mind, all I really knew were very simple rules of thumb, and I fixed what dozens of others before me could not.

Here's what was going on: The water was moving so fast, that created turbulence. In fact, it's quite possible that as the water in the cold coil headers was moving through, it did not go 'into' the coil, but was moving so fast, it was 'sucking' water the wrong way through the coil . . . Much like a venturi action, then possibly recirculating within the coil.

Probably the same thing in the chiller barrel. So much turbulence, not all of the tubes full of refrigerant came into equal contact with the water flowing through them.

So . . . Maybe the same thing is happening in your system. Ignorant techs through the years kept opening the balancing valves thinking more flow was better. Just something to think about.

Maybe just slowing the water down will give you the additional cooling you need. There are special instruments to measure the flow that require special fittings. The of course, the balancing valves, commonly called circuit setters.

 

Lord Kelvin's wave theories make interesting reading. They apply to ship design as well as heat exchanger design. In a chiller barrel you want Some turbulence - so long as you still have laminar flow - to break up the boundary layer at the tube surface. Unless the boundary layer moves it acts as insulation on the tube: between the tube and the flowing water. That defines the lower limit of proper flow rate.

On the other hand the flowing water must be in contact with the entire tube - so you can't have excess velocity or the flowing water does not come back together on the downstream side of the tube. Instead it leaves an area of essentially still water behind the tube So the downstream 30-40% of the tube diameter exchanges little to no heat. Just before those downstream eddy currents break away from the main water flow defines the upper limit of proper flow rate.

PHM
--------

 

Is this customer good friends?

You are spending a lot of time trying to redesign their HVAC system. You might be setting yourself up for a law suit if things go south.

I would have an engineer get involved to take some of the guess work out and spread out the liability.

Be helpful to know more about the chillers and the sequence of operation along with how the system is controlled. How big the place is, the CFMs your dealing with etc.

what size chill water coils you have, their rating. Sounds like they are not big enough. For the the changes they are doing.

Some thoughts come to mind like, can you run colder water temps, can the chiller handle 34* water using glycol. The chiller Manufacture will have those specs. Running chilled water through heat coils not good idea, IMO. heating coils not designed for that. Any concern with RH% or mold?

If the original system was designed for space as intended and now they are changing the space design and usage. there are many other things to take into account. like what are your load calculations?

anyway just be mindful, trying to be creative can cost$$ a some point when the money gets thin the customer will want to see results.