On this forum it was replied recently that "pump/fan" energy aside, the envelope internal surface temperatures are higher for a radiant system and therefore more heat will be lost through the envelope. The benefit only becomes apparent when you sink the air thermostat temperature setting (which is possible whilst retaining the same operative temperature) which then negates the extra heat losses through the thermally warmer envelope on non-heated surfaces. It is known that water with its thermal capacitance is a far more efficient energy transport medium, so you should see energy savings on the fan/pump side of things.
That being said, both systems are sensitive to correct or optimized control stradegies. For example, hydronic radiant systems are not controlled to counter high sporadic load spikes, where as an air heating system can. This makes both systems reliant on how occupants behave. Occupants behave differently dependant on which system they have.
The pump/fan pressure drops need to be pretty real for both systems... Static pressure drops and changing static pressure drops... it could get really complex.
ASHRAE journal had an article (month before last?) where a building in India was symetrical and each have optimized systems and controls for the repective VAV and radiant solutions.
Mit freundlichen Grü�en- Sent from my iPhone (excuse the brevity)
i. A.
Jean Marais
b.i.g. bechtold
Tel. +49 30 6706662-23
On 21.07.2014, at 21:26, "HJ wanghaojie630@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
I use E+ to calculate radiant system compared to traditional VAV system.
The results showed that radiant system uses more heating energy but less
cooling and energy. (of course less fan energy and more pump energy). In
total I could see some energy saving but I would assume this will
diminish in a heating dominate climate. I wonder what is the energy
benefits of a radiant system? I could understand the heating energy
increases because we have more envelope loss. But why then the cooling
energy decrease? This looks like a little inconsistant to me.
HJ
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