PICV valve and it's impact on fan coil 2

[saeedplc]

Hi experts

A question has occupied my mind please clarify it for me:

As you may know pressure independent valves(PICV) have a dial on themselves to adjust maximum flow according to the load characteristic, it is in fact a balancing valve sitted inside the PICV
Now my question is that what will happen if I adjust it uncorrectly, higher or lower value than the load, suppose it is a fan coil controlled with PICV
Will the valve not correct adjusting affect the fan coil performance or not?

Regards

 

[EnergyProfessional]

Based on what are you controlling the valve? discharge air temperature?

By dial, I suppose you mean one of those that get field-adjusted by limiting actuator travel. So you have a 0.5 gpm, 1 gpm and 1.5 gpm setting etc. that dial would set the maximum flow (or actuator travel. Up to that maximum, you still can modulate.

More common are the ones without such dial, and you buy it in whatever setting and the actuator can go full stroke. there also is the type with built-in flowmeter and you give a signal on how many gpm to modulate to. so we have at least 3 types....

You fan coil has a design flowrate for specific air conditions and desired dT. If you set (or select) the wrong flow PICV, you have too low or too high dT.

I think you have to provide much more information what you have or plan to have.

 

[saeedplc]

The fan coil is controlled by room temperature and the PICV valve is Green type from flowcon company,controlled by 0-10 volt
The dial is limiting the maximum flow from the load by narrowing the space of the valve cartridge
Does bad setting of the maximum flow affect the room temperature control or it doesn't?

Why should the maximum flow of the valve be
the same amount of the fan coil maximum flow?

The cartridge of the valve is like below.

 

[EnergyProfessional]

Sounds like you have a modulating actuator and the PICV have a preset for the flow. Each of the numbers represents a flowrate (I wish they would write that on, but yo have to look that up int he spec sheet). Also sounds like your FCU is just on/off. So when heat is needed, the fan starts and the valve opens 100%.

to have the design capacity, the water flow needs to be at or slightly above the design flowrate. So you need to set it close to that. So check the FCU schedule what flow is needed. The designer should provide that info. If too little flow, you lose some capacity (i.e. air will be colder), if too much flow, your dT will be low and you waste pump power. It is not different from any other type of valve.

Of course, setting it wrong will have negative impact. Assuming the valve is in series to the coil, the flow of the coil will equal flow through the valve. I don't see a real scenario where the flows would differ.. that is what a control valve does.

 

[saeedplc]

Yes the actuator is analoge type (0to 10v) and the fan coil is 4pipe type
Two picv valves are used to control cooling and heating coils
The valves are controlled from BMS system and a dedicated controller from siemens. The actuator percentage is controlled by the room temperature but the problem is that the room is controlled improperly and occupants claim they feel too much cold or too much warm.
I decreased the flow by closing a ball valve more befor the picv valve. And the problem mitigated so
Do you think it is more related to the bad adjusting the valve's maximum flowrate or it has nothing to do at all.

It would be appreciated to correlate the flowrate setting according to the case what I mentioned.

 

[EnergyProfessional]

Too cold or too warm? Do you have actual temperatures? I ride my bike in summer with short pants and t-shirt and sweat, and others also riding, but with long pants and jacket. Apparently they still feel cold at 90°F, while I feel warm. Without actually measured objective data you know nothing.

Do you have the design data for the heating and cooling coils? Does the fan speed adjust or is it constant volume (CV)? If CV, I would be concerned about dehumidification if cooling is controlled by chilled water valve only. But again, you need actual data, like dew point etc.

If it is too warm or too cold, are the valves at 100%? Do you know DAT and compare that to design DAT?

 

[saeedplc]

Thank you so much for the reply

To be honest there is neither data available from the designer nor any diagram.
You are completely right I need to get some
actual value then decide about the situation.
Dear @EnergyProfessional could you please let me know how a fan coil should be controlled by assuming it has variable speed capability Fan and the modulation control valves on the coils?

 

[EnergyProfessional]

Does the FCU have a variable speed motor (e.g. ECM)? Do you have discharge air temperature sensor?

If you have that, or can add it you could do this:
- cooling: control fan and valve to have DAT at 55F or below. Increase airflow if more cooling is needed, while keep opening the cooling valve to still maintain 55F. You need low temperature to dehumidify.
- Heating: kind of the above, but with say 90F DAT. If you have high ceiling diffusers you don't want to discharge too warm!!!!!! Unfortunately some heating systems are designed for over 100F and then you have a hot ceiling, and cold occupants (warm air rises)

Obviously this all assumes your coil, fan and hydronic system have the capacity for that space.

Basically control it like an AHU.

 

[saeedplc]

If I have understood well you mean both the fan speed and the valve's position should be controlled by the temperature sensor inside the room?

 

[EnergyProfessional]

Correct. you want to make sure you maintain a specific DAT (or a small range). For cooling this is important to make the air cold enough (to dehumidfy, unless you are in Arizona or so). For heating you want to avoid stratification unless you have very low ceiling or floor diffusers. but you should consult the design documents to find out how the designer sized it and what they prescribed. the operator also may have to make adjustments if on cold or hot days the initial setpoints aren't enough. and hope the FCU in principle is large enough.

Limiting DAT may seem counter-intuitive if you have heating problems. but believe me, I've seen cold rooms where the ceiling was a baking oven and reducing DAT resolved the problem.

Keep in mind, I know nothing about the system. I'm just giving general advice based on what I often see to be the problem and based on what you revealed.

 

[MedicineEng]

Are all occupants complaining about being all cold or all hot or some are feeling cold and others hot?

If it is the latest, have a look on the diffuser distribution and where occupants seat. It might be an air distribution problem.
In my own office, I have the air supply diffuser almost right above my seating area, so I had to use the very high tech solution of stuffing with a piece of armaflex the side of the diffuser that was directly blowing cold air into my neck...problem solved.