Many building owners are considering adding in suite air conditioning to their buildings to increase the value and drive up revenue. A common solution is to use fan coils, which source their heat from an existing or retrofitted central boiler plant and their cooling from a new chiller. The heating and cooling is delivered to each unit via a hydronic loop which circulates water to the fan coils. The fan coils deliver forced air into each suite controlled by individual thermostats. The issue with fan coil systems is that the addition of a chiller increases operating costs significantly.
An option that’s becoming increasingly more popular is the water sourced heat pump – the most energy efficient HVAC system on the market. The main difference between a fan coil system and a water sourced heat pump system is that the cooling and most of the heating is sourced at the in-suite heat pump itself, not from a central plant.
In the heating season, the heat pumps extract heat from the hydronic loop and pump it into the suite. When more heat is required than is being generated within the building and most units are operating in heating mode, supplemental heating is supplied from a central boiler plant. The existing boiler plant in the building can be drastically reduced in size since the system requires substantially less heat supply.
In the cooling season, the heat pumps extract heat from the suites and dump it into the hydronic loop. When most of the units are in cooling mode and the heat isn’t needed elsewhere in the building, the heat is rejected from the loop using a fluid cooler. As opposed to a chiller, a fluid cooler comes at a much lower upfront and maintenance cost.
The true potential of the system is seen in the shoulder seasons, when some units are in heating mode and some in cooling. instead of being wasted, heat is just being moved from one place in the building to another through the hydronic loop. Neither the fluid cooler or the boiler plant would be running. During this scenario, the system is operating at its maximum efficiency. As opposed to a fan coil system, where changeover from heating to cooling is required in the shoulder seasons and you can only operate in heating OR cooling mode depending on time of year, the water sourced heat pumps can run in heating AND cooling mode all year long. This makes the system very attractive to tenants.
The best part is...when this system is paired with sub metering, almost all of the operating cost is passed on to the tenants since most of the energy used is coming from the in-suite electrical panels instead of a central plant.
If sub metering is not an option, then a hybrid fan coil/ heat pump is the next best option. The units act as fan coils in the heating season, sourcing heat from a central boiler plant. Then, in the cooling season they utilize the heat pump and fluid cooler system described earlier. This system would reduce total operating costs by utilizing cheaper natural gas instead of electricity for heating.
To learn more about these systems, contact Mann Engineering, your energy experts!