heat recovery

koen.govers · Posts: 80

I've tried to use the heat recovery in the new beta version of DB.

I can't notice any difference in ventilation loss when the heat recovery is on..

And what do I have to put in the minimum outside air flow rate box ?? The nomainal air rate of the mechanical ventilation ?

Koen

Andy Tindale · Posts: 1198 Location: Stroud

Koen,

I would expect the heat recovery to reduce heating and cooling loads, but not to affect the ventilation loss which relates to heat loss due to cold air entering through windows and the fabric. This because it simply preheats/cools outside air before it enters the air handling unit, easing the load on the heating/cooling equipment.

The minimum outside air flow rate is the minimum flow of air into the house required for ventilation. If it is a constant volume system, then yes this is the nominal air rate of the mechanical ventilation. You can find out more about the meaning of this data in the on-line help.

Regards

Andy

koen.govers · Posts: 80

Andy,

it's still not clear to me. When I alter the mechanical ventilation rate, the 'steady state external ventilation' loss in the heating design alters in the same way. That's normal.

I would expect that I can also reduce this loss by using the heat recovery?
Using heat recovery, I can minimize the installed power. No?

koen

Andy Tindale · Posts: 1198 Location: Stroud

Koen,

The heat recovery data is not used at all in Heating design calculations so you cannot use heat recovery to minimise the installed power. I would recommend simply adjusting the mechanical ventilation rate for the purposes of the heating design calculation to account for any heat recovery you wish to use to reduce design heating capacities.

I hope this answers your question.

Best regards,

Andy

koen.govers · Posts: 80

koen.govers · Posts: 80

What I reaaly want to ask Smile

Do I need to calculate myself the minimum air flow ?
As I have different zones (levels) with a different occupation, I need to calculate the minimum air flow for each level ?

Koen

Andy Tindale · Posts: 1198 Location: Stroud

Koen,

The minimum flow for compact HVAC systems is set at building level once only. As you say, it is calculated by multiplying the maximum number of people in the parts of the building serviced by the system by the 'minimum flow per person' data on the activity tab. It is entered in m3/s.

When an economiser is selected, EnergyPlus modulates between this minimum flow rate and the maximum flow rate, which by default is calculated as the sum of the zone maximum flow rates. When no economiser selected it uses the minimum flow rate directly.

So this minimum flow rate is an important parameter for calculating

a) heating/cooling energy consumption due to conditioning of ventilation air and

b) fan energy consumption.

Starting with DesignBuilder version 1.2.0.030, you will also have the option to define maximum supply flow rates in each zone when using Compact HVAC systems.

So the effect of heat recovery should be visible in reduced heating and cooling demand.

I hope is explains it.

Regards,

Andy

koen.govers · Posts: 80

Andy,

so I don't have to choose 'heat recovery' at each floor level, but only at building level ?

What do I have to write in the 'minimum outside air flow rate' at the levels ? Filling in '0' gives an error....

Koen

Andy Tindale · Posts: 1198 Location: Stroud

Koen,

Sorry, in my reply to your previous questions I assumed that you are modelling a VAV or a multizone unitary system. If you are using a single zone unitary system then heat recovery and minimum outside air flow rate data is specified for each zone.

The minimum outside air flow rate should be entered as the actual mechanical ventilation outside air flow as defined on the slider in ach or as l/s/person on the activity tab. Note that the units are m3/s.

If this does not answer it, please send your dsb file so that I can see what you are trying to model and give you more targeted advice Smile

Regards,

Andy

koen.govers · Posts: 80

Andy,

I can only choose heat recovery in compact mode. Can I simulate a bypass for the recovery with the economiser?

Koen

Andy Tindale · Posts: 1198 Location: Stroud

Koen,

Here is the reply from EnergyPlus support:

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