2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
(OP)
In a situation where you have the system as stated in the thread subject, how is it possible to use the hot water changeover for each unit without having an outrageous LAT or delta T for when the system is in hot water mode. The selected cooling coil for the units and EWT for heating(180 to ~160) make for these numbers to be too large.
In order to get the LAT needed for heating, some units are going to have to pump a significantly low GPM and in turn have a delta T of near 100F.
In this case there is only 2 options I can think of:
1. Scrap the changeover if possible and go electric heat.
2. Select a 4pipe FCU and use control valves to flow from the original 2 pipe into the heating coil when needed.
For the 4 pipe there still is the issue of the changeover being manual, so how would the unit know that the water coming in is heating or cooling? (water temp sensor somewhere?) On top of that, even if it did know.. when there is a call for cooling, it simply wouldn't be there in heating season, and vice versa in cooling(though there is baseboard for the heating application when in cooling season)
Anyone have any insight into the issue?
Thanks
In order to get the LAT needed for heating, some units are going to have to pump a significantly low GPM and in turn have a delta T of near 100F.
In this case there is only 2 options I can think of:
1. Scrap the changeover if possible and go electric heat.
2. Select a 4pipe FCU and use control valves to flow from the original 2 pipe into the heating coil when needed.
For the 4 pipe there still is the issue of the changeover being manual, so how would the unit know that the water coming in is heating or cooling? (water temp sensor somewhere?) On top of that, even if it did know.. when there is a call for cooling, it simply wouldn't be there in heating season, and vice versa in cooling(though there is baseboard for the heating application when in cooling season)
Anyone have any insight into the issue?
Thanks





RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
What your missing for the thread, is the changover period. My energy code requires a 4 hour no heating no cooling changeover period (according to OA), so the system temp can reduce naturally so you dont shock the chiller and dont waste energy.
knowledge is power
RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
I can see a two pipe working when OSA temps fall and you can have a setback controller, controlling water temp based on OSA temps. The FCU would need to have a danfoss valve or something sensing room temp controlling the valve.
But depending on the sun, some days you will require some heat and some cool. will piping be zoned? will there be interior supply fans?
electric heat could cost as much in the long run. should do cost analyses.
RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System
1) Strap-on water temperature switches are found often on these units to reverse the action of the thermostat.
2) Use caution at changeover time from heating to cooling. If your building piping is full of 180°F water, you don't want to immediately dump that through chiller tubes or you'll be buying a new rupture disk and load of refrigerant.
3) Explain in writing to the building owner that there will definitely be uncomfortable spaces during mild weather. Make him or her sign off on it in the presence of a notary and keep a dozen copies in a dozen different places.
Best to you,
Goober Dave
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RE: 2 Pipe Chilled Water/Hot Water Changeover Fan Coil System