Psychrometrics of Local cooling units

[johngrig]

Hello everyone,
I am new to the field of HVAC. I want to resolve some of my questions through the following example. Let’s assume that I have a space that is 50m3 and has a sensible cooling load of 5 kW and a latent cooling load of 1.5 kW. If I want to install a local air conditioning unit, either VRV/VRF or a water fan coil unit, how is the process described psychrometrically? how do I know if the unit covers my needs, considering that catalogues characteristics for VRV systems refers only the total cooling, whereas for water fan coil units, the sensible and latent heat are specified separately for certain temperature conditions?

If I have calculated the loads of the space at different indoor wet bulb and dry bulb temperatures, and the local units have cooling capacities at different conditions from those of my space, how will I know if they cover my needs?

Thank you in advance.
Sam

 

[goutam_freelance]

Conventional fan coil units are designed for a particular design condition. For off-design conditions, one needs to apply correction factors on manufacturer-published cooling capacities.

Whereas in VAV/VRF systems, the total cooling load is the limiting factor. The system can possibly take care of various combinations of sensible/latent cooling and different indoor conditions of different rooms automatically provided the total cooling load of the system is not exceeded.

VAV/VAF systems have higher efficiencies when the outdoor/indoor conditions and cooling loads are variable as they control the refrigerant flow depending on load conditions saving operating power requirements.

However, for a single zone with approximately fixed sensible/latent loads, conventional fan coil units may be more economical.

Regarding the last sentence:

I have calculated the loads of the space at different indoor wet bulb and dry bulb temperatures, and the local units have cooling capacities at different conditions from those of my space, how will I know if they cover my needs

Generally, you need to check the tables published by the manufacturer for the selected model of FCU regarding corrected cooling capacities. This needs to be done for all the zones having different indoor conditions and having separate FCUs.

A more detailed description of loads and indoor conditions is required for a more accurate reply.

 

[johngrig]

In a space, let’s say I have a 10 kW sensible cooling load and a 3 kW latent cooling load. The design temperature is 24 degrees Celsius, and the design relative humidity is 50%. The manufacturer provides a VRV indoor unit with a total cooling load of 15 kW, wich calculated for indoor temperature of 27 degrees Celsius DB and 19 degrees Celsius WB. How can I know if it will meet my requirements?

And something else . Generally where can I find information for paychrometric processes for local vrv/vrf unit , local water fan coil and heated recovery units?

What I want to achieve is, if I know the room volume, the sensible load, the latent load, and the design conditions (desired temperature and relative humidity), to determine which indoor unit to select, whether it is a VRF or a water FCU and how to use correction factor for mine design conditions( temperature humidity etc). If there is any guideline for this, and you could provide it, I would be grateful.

 

[goutam_freelance]

For VRV units you can contact Daikin sales.

For FCU you can approach any reputed company like Carrier Aircon etc.

This will be the most direct approach.

Alternatively, you can contact a reputed local HVAC Consulting company.