HVAC Terminal Control > Motion Sensing Thermostats in Suites

Existing Conditions

Electric control valves and basic electric thermostats already exist.

The existing thermostats are simple low-voltage electrical units that attempt to maintain a constant space temperature at all times. Many are not working, meaning that the suites are fully heated throughout the heating season. Those that are working are fully adjustable by the tenants, and do not reduce heating when doors or windows are open or when the suites are unoccupied.

During the warmer months, tenants leave the air conditioning on all the time, even when the suites are not occupied.

Retrofit Conditions

Modern "smart" thermostats, available from a number of vendors, will reduce the ability of tenants to overheat their units [or use air conditioning when it is not needed]. By incorporating motion sensors and magnetic window/door contacts, the new thermostats can respond to conditions in the suites. They will set the space temperature back when a suite is unoccupied, and can disable heating when a living room window or balcony door is open. These thermostats are electronic devices with many internally set parameters, such as:

•	minimum allowable suite temperature

•	limits on the temperature band for occupant adjustment

•	unoccupied time delay before setback

These parameters can be accessed by the Owner through a portable PC or internal DIP switches, but cannot be adjusted by the occupant.

While installing the thermostats, the contractor will have to test the existing control valves and low voltage control transformers. Some of these parts will have to be replaced, and an allowance has been made in the project cost for this work.

The installation should include a prior "training" period where occupants and the superintendent are told what to expect, and give a basic outline of how the units will moderate space heating. The Owner should also expect a period of increased concern while tenants learn to accept the new thermostats. Suites with elderly or physically disabled tenants will require special adjustment to allow higher space temperature setpoints. Field experience has shown that the first heating season will be a period of adjustment and that concerns will settle down to a normal level for the second heating season.

Further Benefits

Application Details

Issues and Concerns

Most jurisdictions require that the building owner provide a certain indoor temperature during the heating season. The legislation is generally not specific about whether the level of heating must be available to tenants as needed, or whether is must be sustained even when tenants are not at home. The owner should check if there have been local rulings on this matter, and if not, solicit a formal opinion from the municipality.

No such similar legislation exists for suite cooling (air conditioning).

References

This recommendation is in accordance with Measure HV10 of the CMHC manual on Energy and Water Efficiency in Multi-Unit Residential Buildings and with with Section 6.3 Heating, Ventilating and Air Conditioning Systems of the ASHRAE Standard on Energy Conservation in Existing Buildings.

The CMHC manual on Energy and Water Efficiency in Multi-Unit Residential Buildings can be found online at www.hwbinc.com/495-1003/introduction.html

ASHRAE Standard ANSI/ASHRAE/IESNA 100-1995 – Energy Conservation in Existing Buildings is an approved standard of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., the Illuminating Engineering Society of North America and the American National Standards Institute.

Analysis

As of 2003, Log-One has a “power stealing” unit which directly replaces mechanical contact-closure thermostats. $300 each in quantity, less than $50 for installation and setup where no external contacts are required.

Because the ability to set back heat is limited by legislation and by the time it takes radiant systems to recover from setback, most of the savings are typically on the cooling side. The economic justification is much harder to make in "heating only" buildings.

$500/thermostat installed. Note that there may be more than one thermostat in each suite at present.