RE: [EnergyPlus_Support] Zone FanCoils and an AHU

I live in a condo in Toronto, Canada, with two pipe fan coil system with a auxiliary electric heater in each unit. The air is ducted to the various room of the condo unit with only one thermostat control. Two or more fan coils are used with the unit area is larger than 600 sq.ft., and will have one thermostat per system.

The fresh air intake from the roof is cooled or heated in accordance to the seasonal need. However, the fresh air is not fed to the fan coil. It is fed to the corridor of each floor, and the pressure and the leak through the doors forced the air into the various unit. The positive pressure is a fire control requirement.

When I open the sliding window in my unit I would get more fresh air through the door leak. There vertical risers behind the bathroom and closet walls. Air can leak through there as well.

I understand the air leak can be partially implemented with zone air mixing or be ignored all together.

Because the temperature difference between the common fresh air and the condo unit is small, the HVAC energy calculation without the air actually flowing through the unit is still accurate.

Collecting return air from the condo unit to the roof top fresh air intake is not practical, as the amount of the return air is only equal to the fresh air intake. The washer/dryer and bathroom usually have exhaust fans. The air from these need to be controlled, as the dryer turns on a 3kw heater while running. This heat is not wanted in Summer, when the HVAC is in cooling mode..

There are risers which carry cold water to the roof top hot water heaters. These risers can be the natural heat exchanges for the hot damp dryer air.

In Summer, let it flow up and pull in fresh air into the garage. In Winter, closes the top and let the air warms the garage space.

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The configuration you have described below is very similar to that I discussed with Vinay.

The configuration I proposed to him is attached. The feed back from him was that the idea works, except that the heat exchanger flow rate was unbalanced by a ration of 2:1.

The AHU in the diagram only has a fan. In your case, you would need to have a master zone thermostat linked to the air loop. Choose a corridor as a zone for this purpose. Keep this air flow small, as it is the fresh air only requirement. If the return air is zero, all the fresh air equal to the capacity of the fan will be delivered to the zones, with an ADC:uncontrolled at a preset ratio.

There are choices of returning the zone air to the HRU in the diagram as well.

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In proposing new green buildings, we need to look at heat flow control rather that straight HVAC.

I mentioned the dryer above. In the office environment, the laser printers are also large heat source. Elevators, Kitchen and solar radiation need to be investigated as well.

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: vieira.jose99@xxxxxxxxx
Date: Thu, 14 Apr 2011 16:20:08 +0000
Subject: [EnergyPlus_Support] Zone FanCoils and an AHU

Hello, first I want to thank all that helped me understand a little better E+ on this previous topic: http://tech.groups.yahoo.com/group/EnergyPlus_Support/message/19759

Now I have a 74 zone building and want to simulate one AHU to "treat" the minimum new air for occupancy for all the zones and use FanCoils to "treat" the air temperature so that mean air temperature of the zones are 20慢 for winter and 25慢 for Summer.

What i am tring: Air from the AHU splits to the various zones, then it enters the zone FanCoil, the return air from the zones goes back to the AHU for later on apply recovery mechanisms.

For now I am only looking to do this on two zones, so that it is easier to correct mistakes, then when it is working, its easier to do copy/paste for the other zones. For now I am also simulating for the summer design day.

The problem is that the mean air temperature is outragous, it is above 40慢 for the summer design day. There was no return air from the zone to the AHU, the air was being released by the FanCoil relief outlet node, so I hooked that node up to the air mixer, so that it would return to the AHU.

I have uploaded the .idf to the problem submital section, the link is:

http://f1.grp.yahoofs.com/v1/ABqnTWqT74N-28mPIl7kRupySkocrpNc68HOk3a6kHyyGzAmoXDeVi-g1ZaLd_Xwt1650MFZVHq1eZm43mA1RYZJNQxC15tMDPG-/_Problem_Submittals/Sim1_sem_recuperacoes_duas_zonas.zip

I have put two other zones with the FanCoil HVAC template, so I may make comparisions and later on try to modify it.

The air temperature leaving the AHU must be in the 20/25慢 range, only the FanCoils will warm/cool the zone air.

Can someone point me in the wright direction? What is it that is not working here?

Thank-you
Best Regards,
Vieira

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