May 18, 2017

Does your building have 20% spare capacity in its tenant’s supplementary condenser water loop?

Many commercial buildings have Tenant’s Condenser Water systems to provide cooling water to supplementary air conditioning systems located in tenancies. Often the capacity of these systems is under pressure from increasing demands.

Many of the water cooled packaged air conditioning units installed in tenancies before 2008 use R22 refrigerant. R22 is being phased out in accordance with the Montreal Protocol because of its environmental impact. Ultimately all this equipment will reach the point at which it is not economical to repair and maintain. Given the usual life cycle of these units it is likely that most R22 plant will be replaced prior to 2020.

New water cooled package units installed after 2008 typically use refrigerant R410A. Although the newer technology units are more efficient than their R22 predecessors, they generally require additional condenser water flow capacity per kW of cooling compared to an equivalent R22 unit.

The following graph from a leading manufacturer indicates that a R410A unit requires an average tenant condenser water flow capacity increase of 20% compared to a R22 unit.

The R22 units require an average of 0.05l/s/kWr with the R410A units requiring an average of 0.06l/s/kWr.

This increase in tenant condenser water requirement can have significant implications when applied across an existing tenant’s condenser water system, particularly if the system is already at or near the limit of its capacity.

The following actions are recommended to pre-empt and prepare for this issue:

1. Keep an accurate asset schedule of all equipment connected to the tenant condenser water systems. This should not only list the capacity and cooling water requirement but also the age and refrigerant type of the equipment.
2. Actively track and manage the tenant condenser water capacity allocated to each tenancy. The base building HVAC maintenance contractor can undertake an audit of the flow rates after fit-outs take place and maintain the connected load schedule.
3. Engage with existing tenants who have R22 systems. Many will not be aware that system maintenance may become an issue. This is especially relevant if the systems support critical functions like data rooms. Determine when R22 systems may be replaced to forecast increasing water demand.
4. Ensure that all new tenant water cooled packaged units have solenoid shut off valves fitted. This will help to maximize the overall base building condenser water reticulation system diversity when some tenant systems are not in use.
5. Include in the mid-term capex plan for the base building tenant condenser water system capacity to be increased. This is often a challenging project as the system “uptime” is critical and spatial constraints are common in both risers and around cooling towers. It will often be necessary to carry out a feasibility study to see how this can be achieved in a cost effective and non-disruptive manner.

It should be noted that the overall maximum electrical power load may also increase when an equivalent capacity R410A unit is installed in the place of an R22 unit. Checks and allowances should be made for upgrading circuit breakers and potentially sub-mains depending on the nature, size and number of replacements.