# Trying to use a single zone system to supply two zones



## earshavewalls (Jan 7, 2010)

I have a plan submitted where the engineer is trying to use a heat pump (RTU) that currently feeds zone in another leased space to serve a 'small' independent office TI adjacent to the other unit. They are showing motorized dampers in the new space with local thermostats for the dampers, but the main thermostat controlling the heat pump is in the other tenant space.

I know this is not allowed, but I am having trouble finding the code section(s) to cite. Being in California, it seems that the Cal. Energy Code, section 122 (mandatory measures for controls) would be the only place I can find that is close.

This is NOT a constant velocity system, it is a single-zone heat pump with the controlling t-stat in another space.

Help me to help them, please.......


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## Dr. J (Jan 7, 2010)

Re: Trying to use a single zone system to supply two zones

Why would this not be allowed?  A damper pinching off airflow for zone control is no different than VVT, VAV, Thermafuser or one of the several residential zoning systems out there.   There certainly is no requirement for separate tenants to have separate HVAC systems.

However, similar to VVT, VAV, etc, they still need to meet the requirements that outside air be provided whenever occupied. In the IBC world this is:

_IMC 403.3.3 Variable air volume system control._

_Variable air volume air distribution systems, other than those designed to supply only 100-percent outdoor air, shall be provided with controls to regulate the flow of outdoor air. Such control system shall be designed to maintain the flow of outdoor air at a rate of not less than that required by Section 403 over the entire range of supply air operating rates._


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## north star (Jan 8, 2010)

Re: Trying to use a single zone system to supply two zones

*Dr. J.,*

*In the IMC requirement listed for OA to be provided, wouldn't this neccessitate the motor being activated*

*[ in the one RTU ] to supply the OA to this separate tenant space?  Would Article 430.10(B)(1)  in the `08 NEC*

*be applicable ( requirement of a separate disconnecting means to that RTU motor ) ?   :?:*


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## earshavewalls (Jan 11, 2010)

Re: Trying to use a single zone system to supply two zones

I have spoken with the engineer who tried to design this system. The RTU is controlled only by a thermostat in an adjacent unit. This setup MIGHT work if the OA is stepped up to acommodate the added space and if VVT's are used instead of motorized dampers. This would effectively allow coordination and interaction of the unit with both spaces as far as comfort controls.

In my opinion, they would be better off with a small 1.5 or 2 ton unit to serve this space; or tap into the existing CV system that is in use on the first floor of this building.

They are simply trying to save money, which I fully understand, but using a system designed to provide conditioning for a specific zone to control the environment in another space that is thermally isolated by simply using motorized dampers is not a viable system. To top things off, they are proposing to use two separate RTUs for two separate areas to control the temperature of two rooms within this new space. It just won't work.....the biggest issue is how you will control, effectively, the temperatures and air flow in this separate space with the thermostat controls in a completely separate location.

I believe that we will reach a solution. Hard financial times are forcing some to re-invent system uses in ways we haven't seen.


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## Plans Approver (Jan 18, 2010)

Re: Trying to use a single zone system to supply two zones

This won't solve any code or operational problems.

In a former life in the previous century, I was in property management. We had a 2 attorney partnership break up. They wanted their suite split into 2 separate offices. Easy enough to do, 8 feet of wall and split the electrical to 2 submeters. This arrangement worked fine during winter as the building provided heat via steam radiation, but, when warm weather hit there was only one AC unit and the AC unit electric was on only one of the suites. They sued each other for many things including cost of electricity to run the unit, ability to run the unit when the other was closed, weekend, nights. They finally sued the building for violating the lease based on disrupting their "quiet, enjoyment".  Needless to say we sprang for an additional AC unit and reworked their ductwork - on weekends. They were on the 15th floor of a 21 story building built before 1920. We spent a lot of money, but, saved was the cost of litigation. They both moved out a year.

The bottom line is that system split between tenants won't work on many levels.


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