Water Cooler AHU's and Controls

[Latte]

Hi Guys,
Sorry, This is likely to be a long thread but i got called out to my first water cooled unit with problems and i am now :confused: .

First, what i do know:-. The AHU is made by "Air Handlers (Leicestershire) Ltd. but the phone number on the plates is no longer in use. The unit is controlled by 3 touch screens, one in the boiler room which i think is more of a moniter, one in the plantroom which is the controller and one on the side of the pack. The controllers have Electrotech control design services plastered all over them.

Now the problem, the unit will not get below 24 degree's.
First problem i found was the cold water pump on the side of the pack had tripped. I reset this and checked it and assumed over time it would pull back down - WRONG !!!:eek:

Had another look today, pump OK, cold water showing 9 degrees but when i looked at the AHU it appears to me that the reheat valve is letting by. The control side appears to be OK. The valves are controlled by Trend actuators which have a plunger going into the valves. Now at the moment the reheat valve has the plunger all the way up (Shut) and the cooling valve has the plunger all the way down (Open). Now feeling all three pipes on both, they are the same temp so am assuming they are bypassing and i am getting both the cool and heat coils inside the AHU working against each other.

Now, hear goes, The valve on the top of each valve is a Trend V50/P/26 but the valves have no markings as to manufacturer.

The cooling valve has stamped into the body 1 1/2" PN16 B G25 and the reheat Valve as stamped on it 1" PN16 B G25.

Does anybody know what make these valves are as a need to get some. Secondly, Changing them doesn't look too bad as there are shut off valves on all three pipes on them both but i assume i need to shut the pumps off. The cooling side i already know the pump is beside the pack but the heating pump i havn't found yet, any idea's what i am looking for.

Well i think thats it, too many questions, too stubby fingers to keep typing

Regards

Fatboy

[frank]

Hi Raymond

The Trend controller has many settings (done via laptop) and without this info you cannot make any judgement as to how the ahu is performing.

It is quite common for both the cooling coil and the reheat coil to be in use depending on the low limit set point within the Trend software. By this I mean, say the room is over heating so the Trend calls for cooling, the compressor(s) kick in and the air temp goes down. Quite normal. Lets say that the ambient temp is quite low so the air off coil temp starts to drop to say 13 or 12C. If this is below the low limit set point the Trend will open the reheat valve to increase the off coil temp to prevent really cold draughts, say bringing the leaving temp up to 16/17C.

As the Trend can't offload the compressor (on/off comp) it has no other choice but to try to increase the leaving temp with reheat.

This is a normal way of control and you just can't see it with out the laptop and Gateway software.

[techguy]

Hi R
Quiet right frank its not unusual to be cooling and heating similtaniously. If you don't have access to the software try shutting down the flow regulating valve on the heating coil as a temperorary measure. This will get you cooling while you check out the heating valve Check for control voltage to the actuator most trend actuators are 24v supply and 0-10 v dc open ,close with a spring return mechanism.If control voltage is present then the valve is being driven open by the controller and software access will be required to change the setpoints.

If no control voltage is present

The valves may be passing if the actuator has slipped you may need to restroke the valve. Disconnect the motor from the valve and manually close it. test the pipe temperatures with a contact themometer. you should only have flow in the bypass the coil should lock and rise/drop depending on cooling or heating coil in themperature if the valve is seating properly. Then with the power off reattach the Actuator they all drive full closed on power off. Try this with both cooling and heating valves. If you have any change in coil temp. when the valves are manually shut. you will have to change the valve. Be carefull both water systems may be pressurised so be sure to turn off any pressurisation pump sets, autofill valves and release the system pressure before you open any mechanical connections Remove the valve and bring it to a mech supplier they should be able to supply you with a replacement. (some valves can be dismantaled and the seats can be cleaned if this is the case it will be obvious when you remove the valve.)

best of luck
T

[Latte]

Hi Guys,

I havn't been back to site yet but a couple of questions :confused:

On the cooling side i realise how it works and the gas cooling the water etc but how does the heat side work. Is there a gas boiler somewhere with a pump for the water on it ?

Now - Assuming the valve IS leaking by and it is not a control failure could i as a temp measure close off the hot water return pipe from the hot coil or is this likely to burn out the water pump (Wherever it is).

Regards

Fatboy

[frank]

Hi Guys,

I havn't been back to site yet but a couple of questions :confused:

On the cooling side i realise how it works and the gas cooling the water etc but how does the heat side work. Is there a gas boiler somewhere with a pump for the water on it ?

Now - Assuming the valve IS leaking by and it is not a control failure could i as a temp measure close off the hot water return pipe from the hot coil or is this likely to burn out the water pump (Wherever it is).

Regards

Fatboy

Hi Raymond

Yes there should be a boiler supplying heat to the reheat coil. Shutting off the flow to the coil should not cause any damage to the pump as the coil can be cut off by the control valve during normal operation. Is the valve 3 port or 2 port?

Why don't you take some air off temperature readings with the valve in it's present position and then when you isolate it. This should give you a good indication of what is happening. Or you could measure for control voltage to the valve head. Some, but not all have a 24v supply and then a 0-10v DC control signal. If you measure 5v DC then the valve should be 50% open etc.

[jamcool]

on some units the hot water side is used for humidity control there might be a bms(building managment system) in the building some where with some stats that regulate the hot water side and also the cold water side as was said if u take off the 24 volt from the actuator it should close or u could look for a disengage clutch a button or a level that would free up the actuator so u can close it manual.

[Temprite]

Hi Guys,

I havn't been back to site yet but a couple of questions :confused:

On the cooling side i realise how it works and the gas cooling the water etc but how does the heat side work. Is there a gas boiler somewhere with a pump for the water on it ?

Now - Assuming the valve IS leaking by and it is not a control failure could i as a temp measure close off the hot water return pipe from the hot coil or is this likely to burn out the water pump (Wherever it is).

Regards

Fatboy

Turning the heating water off to the valve wont have any adverse affects.
I have done that on many occasions when valves have been faulty while waiting for replacement.
There will most probably be a bypass valve somewhere in the loop water.