Hi Group, I have a project with only Radiant Floor Heating with Natural Ventilation. I have modeled both baseline and proposed with the baseline HVAC for cooling (the missing system). However, because of the large internal masses, the responsiveness of the radiant system is far slower than that of an air heating system such as in the baseline. This gives me 0 unmetloadhours for the baseline case, but 290 unmetloadhours for the proposed design case. Although I find the unmetloadhours in bounds at under 300, the differential with the baseline is more than 50. Increasing the capacity of the system has no effect, obviously...a radiant surface at max temp can only have a certain maximum heat transfer due to free convection limitations. Q) is it therefore the "right" thing to do to include the heating system of the baseline to catch these small unmetloadhours? Or should I try and explain away the large deviation between designcase and baseline case for unmetloadhours for heating? Jean

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Francesco Passerini

engineer

LEEDuser Basic Member

65 thumbs up

Tue, 05/28/2013 - 09:24

Hello Jean, I solved a similar problem working with the control of the radiant floor. It was something similar: during the night the setpoint temperature was 15°C and since the 9.00 the setpoint temperature was 20°C. The problem with the not met sepoint temperatures was during the morning, therefore I anticipated the “diurnal mode” of the heated floor in the last hours of the night (obviously without changing the zone setpoint temperature; the practical way to solve the problem depends on the used software). Because of the thermal inertia of the heated floor I was able to anticipate the “night mode” in the afternoon. Probably also increasing (in a reasonable way) the supply water temperature could help. I don’t know if working with the control system could be useful in your case. Perhaps your problem depends on too high natural ventilation rates, even when there are very cold outdoor temperatures. In that case you should try changing the management of natural ventilation. I think that the resolution of the problem depends a lot on the used software. Maybe a discussion in the maling list of EnergyPlus could be interesting :-) Regards

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Tue, 05/28/2013 - 10:04

It's a bit more complicated...the culprit rooms are rooms that require per ashrae have high exhaust rate requirements, like a kitchen or WC. The makeup air is currently comming from outside...perhaps the solution is to have the makeup air come from adjacent rooms and setting the AHU for these spaces to circulation only. I'll give it a go. Actually, thermodynamically it makes little difference where the extra ODA is heated, and for the additional effort, I think I'll just include the 2nd system for now.

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Wed, 05/29/2013 - 08:30

Just an update...as the real ODA requirement for my tested WC is zero, I have found that giving the system 3 cooling system a outdoor air requirement of zero, whilst simultaneously pulling the make up air of the required exhaust rate from the adjacent space seems to solve my problem.

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