Hello All,

We're analyzing an HVAC retrofit for a multifamily complex. The baseline building employs electric radiant panels (modeled as baseboard heaters) and there are two considered retrofits.

Option One is to supplement the radiant heat in the perimeter areas with a heat pump that does not feature supplementary heating (i.e., no electric resistance element). However, the original electric radiant panels will be present.

Option Two is to remove the original radiant electric panels and install heat pumps to serve the entire building. We're modeling for a mild climate and the heat pumps can operate well below the anticipated annual temperature lows.

Intuitively, we felt Option Two would save the greatest amounts of energy. However, upon removal of the baseboard heating we noticed that the heating energy consumption increased (i.e., option two was more energy intensive than option one) relative to Option One (although it still remains lower than the baseline building). One theory is that removal of the baseboard heaters requires the heat pumps to produce additional heat to counter the cooler interior skin temperatures. But, we aren't certain so we're curious to hear if any others might have some thoughts.

For reference, all equipment capacity is auto sized, so there aren't unmet load issues. Also, the actual building heat loads (as per the PS-A reports) are identical across all cases, as would be expected. Lastly, the heat pump models do reveal the anticipated increased loads due to ventilation and cooling, so we know these aren't the cause.

Thanks!

Bryan
_______________________________________________________________________
Bryan Russo