DX Split Hot Gas Reheat

[05542209]

I have several 20T (two stages) DX splits installed on gym. I need to improve dehumidifacation which I plan on doing by adding Hot gas bypass(rawal device) and hot gas reheat. I desparately need your help with the following questions/concerns:

1.Should I do on/off reheat or modulating? I'm a bit concerned that with on/off temperature swings my be enough to cause discomfort in the space. However, the simplicity of the on/off is the way I'm leaning.
2.Every Hot Gas Reheat installation I've even done has been on packaged equipment where I route my hot gas/liquid leaving the HGRH coil back to the discharge line. However, this being a split I'm considering routing it back into the evaporator. I've been told, by several people, that routing hot gas/liquid to the evaporator will lessen my ability to dehumidify by reducing coil temperature. This seems counterintuitive to my but I would like to ask your option.
3.And the final question. I did a search on this forum before posting and someone has suggested adding a liquid line receiver when doing HGRH. Why is it needed?

Thanks in advance for your help,
D

 

[AbbyNormal]

Bard adds a desuperheater coil in series but down stream of the evaporater. On a dehu call without a cooling call a solenoid allows the dishcrage gas flow to split between the desuperheater and the condenser.

When I use hot gas for this type of application, I prefer it to be on off, and such that there is not a lot of difference bewteen the entering and leaving air temps when it is engaged. -- like it blows 77 or 78F air that is dry

I also use hot gas on situations where the latent load is big enough that it is pyschrometrically impossible for a cooling coil alone to give you the correct dry bulb and wet bulb. Example a load with lots of people, (even active ones like a gym or pentacostal church) and lots of outdoor air.

In this case I usually use a small dedicated compressor with an evap and condenser down stream of the main cooling coil. This extra evap gets the dewpoint down to what I need and fan heat (pulling air through three coils) and the hot gas reheat seem to give me a 64 or 65F discharge temperature with a 50 dew point.

Only ever looked at a rawal to modulate capacity on a big oversized constant volume system having a classic part load dehumidifaction project.

Addison seems to be into modulating hot gas.

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[05542209]

Thanks. I agree that temperature swings with on/off reheat aren't major.

 

[AbbyNormal]

you just need to look at what your supply temp is when the reheat is on

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[engair]

Careful of trying to install mod reheat on the system if it isn't R-22. Some of the components you need for 410A aren't ready yet.

 

[AbbyNormal]

this one was made in Calgary

4 trane scrolls on the big coil get air down to about 52F

copeland is connected to an additional evaporator and condesner in series down streams,pulls the air down to about 50 on a dehu call, with fan heat it blows about 65F dry air

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[AbbyNormal]

two more units (except main coil is chilled water) are on route presently, 410A, on/off reheat.

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[AbbyNormal]

so you can do it like this on a split but you typically have at least a small compressor in the air handler

I have a couple units like that in operation down here as well

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[05542209]

Thanks once again.

I cannot add another compressor/evap/condenser due to $. My plan is to have humidistat make the dehum call based on space. If there is not cooling call at the time I would turn stage 1 on and cycle reheat to satisfy the space. If stage 1 is already 'on' on cooling call, i would bring on stage 2 and cycle reheat as above. Do you see any issues with that theory?

Also, do you think liquid line reciever is necessary in this situation?

 

[AbbyNormal]

If stage 1 and stage 2 are equal capacity and independent not a tandem or a semi, you could mimic a york DR series package unit.

Basically add a second condenser coil down stream on the stage 2.

On a dehu call run both compressors but send the gas for stage 2 through the new inline condenser rather than the condensing unit coil.

Look at the "alternate reheat function" on page 7

http://www.yorkupg.com/PDFFiles/261659-YTG-E-1008.pdf

The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install