Client converted 1,100 fixtures from double-ended HPS to LED. Lighting load dropped about 40 percent,
exactly as the vendor modeled. Client is furious because the bill barely moved and they want to know
who to blame.
Nobody, as far as I can tell, but the analysis is instructive.
The lighting reduction is real. What the vendor's model did not include is that HPS fixtures were
contributing a large sensible heat load that the HVAC was removing. Remove the heat source and the
cooling load drops, which is a second saving, but the dehumidification load goes up because the
plants are transpiring the same amount into an environment with less sensible heat to help drive it.
Net effect at this facility is that HVAC energy fell much less than expected and dehumidification
energy rose. Combined with the demand ratchet still riding from the pre-conversion peak, the invoice
barely moved.
The ratchet is the piece the client understands least. They will not see the demand saving until the
ratchet rolls off, which is another five months.
exactly as the vendor modeled. Client is furious because the bill barely moved and they want to know
who to blame.
Nobody, as far as I can tell, but the analysis is instructive.
The lighting reduction is real. What the vendor's model did not include is that HPS fixtures were
contributing a large sensible heat load that the HVAC was removing. Remove the heat source and the
cooling load drops, which is a second saving, but the dehumidification load goes up because the
plants are transpiring the same amount into an environment with less sensible heat to help drive it.
Net effect at this facility is that HVAC energy fell much less than expected and dehumidification
energy rose. Combined with the demand ratchet still riding from the pre-conversion peak, the invoice
barely moved.
The ratchet is the piece the client understands least. They will not see the demand saving until the
ratchet rolls off, which is another five months.