Converting a heat loss calculation to energy use

[RISolar]

HI folks. I am developing a spreadsheet for solar thermal design. Is there a general formula that I could work with that will convert a manual J heat loss calculation into actual energy consumed on a monthly basis. I have experimented with "[Heat loss*24/65-design temp*heating degree days]*correction factor".

I don't have confidence in it and was hoping there is another formula I can use.
Thank you in advance for your help

 

[ChrisConley]

Unfortunetly there is no 'calculate energy usuage from peak heat loss / heat gain' equation.

ASHRAE used to publish a methodology using 'degree-days' and peak load. It was abandoned as being quite inaccurate. If you find an old ASHRAE Handbook (1970 or earlier) you can use it, keeping in mind it was dropped for being inaccurate.

There are a stack of energy modelling softwares out there, many are free, none that I have found are spreadsheet based.

 

[RISolar]

Thanks Chris

 

[marcoh]

How comprehensive is the spreadsheet to calculate the heat gain? If you can work out the heat gain for every hour of a typical day for every month you could guestimate something.

Energy analysis software basically does a heat gain calculation for every hour of the year (ie 8760 calcultions)using the weather data for a typical average year. As with anything simulation are only as good as the assumptions that go in it, so a very hot year, or very cold year could have a significant difference to the calculated theoretical energy analysis

In my climate as a first rough guess for a system operating business hours I assume an average 45% cooling demand for the number of operating hours. EG a 1000kWr chilled water system operating 12 hours day/5days per week/ 52 weeks per year, annual cooling demand is (45% x 1000kWr x 3120 hours) / (6.0 NPLV) = 234,000 kWh electrical.

 

[RISolar]

Thank you Marcoh,
This is not an equipment sizing spread sheet. I can get RETSCREEN information to average out the solar gain from my solar collectors each month. What I'm looking for is an average energy usage per month. I have a manual J heat-load calculation to work with. The idea is to off set the energy use with the solar gain and show this on a spreadsheet.

If I were to run my manual J program on an hourly basis, changing the design temp to represent the average temp on that day at that hour, that may work, but I was hoping for an easier way.

What do you think.