morning Warm-up issue with water source hybrid geo system

[hvac1223]

We have struggled with building warmup issues during the morning keeping the temperatures warm on cold days below 40 degrees outside.

The facility is heated and cooled with a vertical loop geothermal hybrid system. The building uses a centralized pumping system from the geothermal well field to the mechanical room and out to the buildings water source heat pump terminal units with a return loop using a cooling tower for supplemental cooling. Three (3) pump water throughout the buildings to zones of water source heat pump terminal units. One (1) of pumps is used for backup and is sized at smaller rate of 102 GPM. There are a total of seventy six (76) terminal units ranging from 2.3 to 45 GPM. The water is pump to and from the well field using two (2) pumps sized at 53 GPM. A cooling tower is used for supplemental cooling. Building flow is 330 gpm. This flow is based on the calculated cooling load requirement. Well field flow is 106 gpm. This is flow that is lower than the building flow is based on the calculated heat requirement of the building. The building pumps run when the building is occupied and whenever any heat pump is running to maintain night setback temperature. The building pumps shut down during night setback when no heat pumps are running. The geothermal pumps run whenever the building loop is below 60deg or above 80deg. The pumps start as soon as there is a call for a heat pump to run and there is a delay start on the heat pump itself to allow the water flow to be established. The owner would like a night setback to 55deg but it is now set at 65deg since the building would take too long to recover from the lower setback. All piping throughout the building using the geothermal system is insulated. The well field has 200 foot deep wells with 1” pipe and a reverse return loop. The well field is not sized for future additions.

Location: Central Kentucky
Area: 50,000 ft2

Any suggestions would be greatly appreciated

[acwizard]

Night setback is always a problem with geothermal. In your case you need the water source heat pumps running in order to take advantatage of the geo loop. How are the terminal units controlled and is the building controlled by a total energy management setup. I would think that some thermal storage would help . Possibly solar could be added to induce more energy into the loop. How is the building being ventilated, and how much exhaust air is being dumped.

[tedkidd]

The problem may be with the building owner, not the system. Sounds like hes jumping to ignorant assumptions and needs some education. Will this be possible, or is he untrainable? start with some questions:

Why does he want a night setback?
Oh? How much savings has he calculated?
Oh, just assuming it will save?
Try to get quite a few questions answered before putting the teacher hat on. He needs to be softened by some of his own statements to be receptive or it may just be an argument.

He traded his corvette for a freight train. His transportation cost went through the floor, but he didnt realize he couldn't drive it the same.
Talk about cop, stripping too many btu from ground with no recovery, thermal mass and occupant comfort, etc...

More education earlier would have helpful, but he probably bought a product rather than a solution. So his square peg mentality is frustrated by all the round holes.

[AiResearch]

Night setback is always a problem with geothermal. In your case you need the water source heat pumps running in order to take advantatage of the geo loop. How are the terminal units controlled and is the building controlled by a total energy management setup. I would think that some thermal storage would help . Possibly solar could be added to induce more energy into the loop. How is the building being ventilated, and how much exhaust air is being dumped.

acwizard right on the track. If the system is on a good digital control , it may not have the optimal settings. These can make or break the best system.

Yes , how is the ventilation control? Does intake and exhaust air shut off during un-occupied?

This system must have been engineered to have sufficient capacity with correct entering water temps (at term units) , no actual test numbers were listed and wshp's with entering water temps of 60* or greater , will give excellent heating in the southern regions. If that cannot be achieved for the MWU , then thermal storage like wizard says , is an outstanding option , a small boiler could come on at night and heat the vessel to maybe 70* and wouldnt run much to achieve that. Then during MWU , nice warm water would be available and the equipment should perform well.

If the equipment run time during MWU is near that of night heating without NSB , then an additional heat energy source is needed. Boiler and insulated storage tank is a powerful way to go , while still taking advantage of un-occupied space temperature setpoints.

[AiResearch]

Geothermal is much geographical. Not all area's are good canidate's. Usually , supplemental cooling to the loop is not needed , heating more common.

[mseng]

With a geo system you do not want to do a night setback. Because the unit will turn on then find out it cannot make set point so it will bring on 2nd stage then auxiliary heat costing you money. Effetely losing all you are saving putting in the geo. If you leave for a week it is still questionably if you are saving anything.