Cooling consumption during winter

asked 2017-06-02 10:05:23 -0600

marinafs1
81 ●5

updated 2017-08-06 07:23:39 -0600

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hello everybody.

I'm having trouble with my model. I'm doing the simulation for a 80 m2 single home in Rome, Italy. My problem is that I get cooling consumption even in the winter. I thought that this could be due to the high solar radiation heat gain, so I added shadings, blinds and also I modified the model on Sketchup to add shading surfaces. Unfortunately this didn't solve the problem as I still got cooling during the winter. Also, (but this is a different problem), the fan flow is ridiculously high, up to 25 kg/s. I had to hard-sized the maximum flow to 50 m3/s, because if not, the system would not reach setpoint temperature for heating.

I tried everything so I decided to set the cooling thermostat setpoint for the winter high, (50ºC), and I still get cooling during the winter! I don't know what else to try! Please help

Comments

sounds like you're having an issue with system sizing, and that the system is sizing to meet an unrealistic internal load. What are you assuming for lighting and equipment power density? If you posted a link to your model, the forum could debug ti really fast.

mdahlhausen ( 2017-06-02 12:08:54 -0600 )edit

Link added! link text

About what you mentioned on the lighting and equipment power density. I am using a fix value on W and then dimensionless schedules. That is supposed to be solved ,since I changed the values of the fraction radiant, fraction visible...to recommended values but I don't know anymore.

Also i get this in the .eio file:

marinafs1 ( 2017-06-02 12:31:51 -0600 )edit

The following error categories occurred. Consider correcting or noting. Loads Initialization did not Converge ..1) very high thermal mass such as very thick concrete (solution: increase max number of warmup . days in the BUILDING object); 2) moderate mass and inadequate space conditioning such that the building keeps getting warmer and warmer on successive days (solution: add HVAC, check buildinl properties, check infiltration is included, make sure HVAC properly controlled);

Infiltration is included, so that's not the problem

marinafs1 ( 2017-06-02 12:34:06 -0600 )edit

3) a soil layer modeled below the concrete slab - (solution remove this layer and read about ground temperatures in the Auxiliary Programs document). This is supposed to be resolved by adding and Energyplus Measure (slab) link textbut bcl is down so I haven't been able to try that yet

marinafs1 ( 2017-06-02 12:36:00 -0600 )edit

If you add a tag like 'openstudio' or 'energyplus', it should send email to the right people on the development teams.

__AmirRoth__ ( 2017-06-02 12:36:14 -0600 )edit

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answered 2017-06-02 15:53:36 -0600

mdahlhausen

9499 ●19 ●11 http://openstudio.net/

The Supply Air Temperature setpoint in the model is modeled as if it were the thermostat temperature, thus forcing the system to have a very high amount of airflow to meet the setpoint. Intuitively, the equipment will produce air much colder or hotter than zone air to cool/heat the zone.

image description

To fix this model, I changed the supply air temperature setpoint controller to SingleZoneHeating and include a SingleZoneCooling after the cooling coil. This will adjust the supply air temperature to meet the load in the space, and gives a more reasonable (but still high) 0.97 m3/s (2000 cfm) fan sizing.

But the larger question is what sort of HVAC system do you want to model? Right now, you are modeling a VAV system with heat recovery, heating coils served by a heat pump hot water loop, and an air-cooled chiller serving a cooling coil. This is not a typical system for a residential project, and the resulting pump energy is half of your total annual electricity use. I think what you want is a zonal heatpump with an ERV, both of which are ZONE HVAC objects available in the thermal zones tab.

Also your model is using 2.9 m^3 (~770 gal) of water per day which seems high.

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Comments

Can you post a link to the model? I am modelling this residential house to get the thermal demand, because this is part of a larger SmartGrid Project. We have choosen heat pumps with TES but about what you said about the HVAC we didn't give it to much thought, because like I said, what we wanted is to get a thermal demand pattern. I'll try what you're telling me to reduce electricity use. Also I will give another look to water use!

Thanks a lot

marinafs1 ( 2017-06-03 05:49:59 -0600 )edit

Hello again. I added the SingleZoneHeating and Cooling as you suggested, but the fan sizing I get it's very similar with the one in my previous model. Also I still get cooling in the winter (even though is less) and now I've seen that I get heating in the summer, so my problem is still not resolved.

marinafs1 ( 2017-06-04 12:53:16 -0600 )edit

If you just want thermal load, just delete the HVAC system and use ideal loads. See posts here and here. Search the forum with the ideal-loads-air-system tag.

mdahlhausen ( 2017-06-04 15:14:00 -0600 )edit

The scope is to get the thermal load but modelling a complete system...So I cannot delete HVAC

marinafs1 ( 2017-06-05 02:46:18 -0600 )edit

The thermal load will be the same whether you model the complete HVAC or not. Anyways - run the model with ideal loads as well. If you still see heating in summer and cooling in winter, then you know it isn't an HVAC problem. Total amount matters too. If heating in summer is << than cooling, and cooling in winter is << heating, then your model is probably performing correctly. Did you delete the main HVAC loop when you added the zonal HVAC systems?

mdahlhausen ( 2017-06-05 11:24:35 -0600 )edit

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