[TRNSYS-users] Air-based PVT-Type 50

[Jeff Thornton]

Ali, 

Is this a real product or have you checked the math on this concept? An
un-glazed collector at 100 C will have tremendous convective and
radiative losses to the environment - in fact you might not even be able
to get to 100 C without some sort of concentration. Even with no wind
and with near perfect solar absorption I'm not sure you can get there.
I'd have to do the math to make sure though. There's a reason un-glazed
collectors are for low-temperature applications. 

Jeff 

---
Jeff Thornton
President - TESS LLC
3 N. Pinckney Street, Suite 202, Madison WI USA 53703
Office: (608) 274-2577 Fax: (608) 278-1475
www.tess-inc.com
E-Mail: thornton at tess-inc.com

On 05/25/2021 11:41 am, Ali Shahrouzian via TRNSYS-users wrote: 

> Dear David, 
> 
> Thank you very much. As you mentioned, there are a number of air-based models available in TESS library (such as types 560 and 563), But I guess they are suitable for low-temperature applications. In fact, I need an air based PVT which produces an outlet temperature of at least 100 C. Furthermore, They are unglazed. Do you think types 560 and 563 are applicable for applications with temperature of around 80 - 100 C? 
> 
> One more question, could I use type 760 as an air to air heat exchanger for high temperature applications, around 80 degrees Celsius. 
> 
> Best Regards, 
> 
> Ali 
> 
> FROM: David BRADLEY <d.bradley at tess-inc.com> 
> SENT: May 25, 2021 11:51 AM
> TO: TRNSYS users mailing list at OneBuilding.org <trnsys-users at lists.onebuilding.org>
> CC: Ali Shahrouzian <ALISHAHROUZIAN at cmail.carleton.ca>
> SUBJECT: Re: [TRNSYS-users] Air-based PVT-Type 50 
> 
> [External Email] 
> 
> Ali, 
> 
> The problem with just changing the fluid specific heat is that the model still won't take into account the impact of the latent heat of vaporization that occurs in air as it passes through the collector. If you're going to approximate an air-based collector using Type50 you at least need to put a psychrometrics component (Type33) after the collector and pass it the collector outlet temperature and the collector's _inlet _humidity ratio since the absolute humidity won't change across the collector as the working fluid heats up. The Type33 will correct the exiting air state when the collector is heating the working fluid. Correcting the air after calculating the collector performance isn't ideal. You also have to be concerned about flow through the collector when there isn't enough solar energy to heat up the working fluid. If the fluid is cooling down instead of heating up (and it certainly can unless your controls specifically prevent it) and it cools down enough that it drops
below the dewpoint temperature then water is going to condense out of the air as it passes through. Again the Type33 will correct the outlet air state and account for the condensation energy but again, it will only correct it after the fact and the correction won't impact the collector's performance. 
> 
> A preferable solution would be that if you have access to it there are a number of air-based PV/T models available in the TESS Electrical library 
> 
> kind regards, 
> 
> David 
> 
> On 05/25/2021 09:05, Ali Shahrouzian via TRNSYS-users wrote: 
> 
>> Hi, 
>> 
>> I'm modelling an air-based PVT system for heating application. Do you think I could use the type 50 as an air-based PVT collector if I specify the fluid thermal capacitance of 1 (kJ/kg.K) instead of 4.19? 
>> 
>> Thanks in advance 
>> 
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> -- 
> 
> ***************************
> 
> David BRADLEY
> 
> Principal
> 
> Thermal Energy Systems Specialists, LLC
> 
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> 
> Madison, WI 53703 USA
> 
> P:+1.608.274.2577
> 
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> 
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> 
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