Posted by *zoe_lithoi* on November 30, 2014, 5:28 pm

Straw-infilled-Pallet Winter Greenhouse.

Greetings,

My son and I are building a 80" x 80" x 8'(tall) 'winter' Greenhouse made o

f pallets screwed together and stuffed with straw for insulation (R10?). I

t has plastic stapled to the inside which should prevent heat loss by conve

ction. The Roof has masonite siding on it in case of rain. We will have 200

of grow lights which will also serve as the primary heat source. The groun

d will be either a heat source or a heat sink (not sure yet.....). The goal

is to keep the temperature above freezing so the seedlings don't die.

The surface area of the 4 walls, and ceiling would be:

A = 4*7*8 + 7*7 = 273 sqft

The heat from the growlights

Hgl = 200W * 3.41 Btu/1Watt-hr = 682 Btu/hr

Hgnd = ground heat will be called:

For now, we will assume that heat from the growlites will enter the ground.

Hrm = heat leaving the room of Temperature, Trm, thru the 273sqft of R10

walls and ceiling to the 20degF outside is:

Hrm = (Trm - 20)degF*273sqft / R10 hr-sqft-degF/Btu] = (Trm - 20)* 27 B

tu/hr

If the room gets new air each hour equivalent to it's volume, then the air-

exchange heat loss for the amount of heat the air in the 400cuft (8'*7'*7')

room absorbs to go from 20degF to Trm is:

Hair = (Trm - 20)degF * 1/55 Btu/F /cuft * 400cuft ~= (Trm - 20) * 5 B

tu/hr

The heatflow equation then, is:

Hgl = Hgnd + Hrm + Hair

682 = Hgnd + (Trm - 20)* 27 + (Trm - 20) * 5

For now, let's assume the heat flow into or out of the ground is 0, i.e.:

Hgnd = 0

682 = (Trm - 20)* 27 + (Trm - 20) * 5

682 = 33*Trm - 20* (27 + 5)

682 = 33*Trm - 660

1342 = 33*Trm

Trm = 1342/33 = 41degF

If the outside temperature was 0degF, then

Trm = 682/33 = 21degF

--- daid seedlings

So we need to look at the ground temperature.

In the above calc's, Trm is between 20 and 40degF. The Ground temperature,

for the southwest (NEvada, Utah, Arizona), 4inches deep (the approix depth

heat can travel in the ground in 1 hour --- see the 'daycreek' thread in th

is group), is about 50degF. So as long as the greenhouse temperature, Trm,

is below 50degF, then the ground is a heat source and supplies heat to the

greenhouse.

-----------------------------

-SAND Heat capacity 2.5 BTU/(F-sqft-in)

-SAND Resistance 0.083 hr-sqft-F/(BTU-in)

From past calculations and real-world example (daycreek.com), ground heat t

ravels about 4inches per hour, so:

-SAND Heat capacity 2.5 BTU/(F-sqft-in) * 4inch = 10 BTU/F-sqft

-SAND Resistance 0.083 hr-sqft-F/(BTU-in) * 4inch = 0.33 hr-sqft-F/Bt

u

The surface area of the ground is:

7' x 7' = ~50sqft

Hgnd = (50degF - Trm)*50sqft / [0.33 hr-sqft-F/Btu]

Hgnd = (50degF - Trm) * 16.5 Btu/hr

-------------------

Now let's include the ground heat in the heatflow equation which again is:

Hgl = - Hgnd + Hrm + Hair

682 = -(50degF - Trm) * 16.5 + (Trm - 20)* 27 + (Trm - 20) * 5

682 = (+16.5+27+5)*Trm - 50*16.5 - 20* (27 + 5)

682 = 44*Trm - 825 - 660

2167 = 44*Trm

Trm = 2167/44 = 49degF

Now, if the outside temperature is 0degF (instead of 20degF):

682 = (+16.5+27+5)*Trm - 50*16.5 - 0* (27 + 5)

682 = 44*Trm - 825

1597 = 44*Trm

Trm = 1507/44 = 34

If a 400Watt growlite were used, and it was 0degF

Hgl = 1364Btu/hr

Then:

1364 = 44*Trm - 825

2189 = 44*Trm

Trm = 2189/44 = 50degF

If there were not any growlites, and it was 20degF outside, then:

0 = 44*Trm - 825 - 660

1485 = 44*Trm

Trm = 1485/44 = 34degF

The lowest daily low temperature in Las Vegas Nv for the month of July is 4

0degF

See: https://weatherspark.com/averages/31890/1/Las-Vegas-Nevada-United-Stat

es

Daytime temperatures are normally in the 50's and 60's.

Using Outside temperature of 40degF, with a 200W growlight we get:

682 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5)

682 = 44*Trm - 825 - 1320

2827 = 44*Trm

Trm = 2827/44 = 64degF

Using Outside temperature of 40degF, without a 200W growlight we get:

0 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5)

0 = 44*Trm - 825 - 1320

2145 = 44*Trm

Trm = 2145/44 = 49degF

So, one might have a thermostat to power the growlights if the temperature

dropped below 45degF.... AND Further, put the growlites on a timer to give

it 12 hours each day (so the plants can get light) during night-time hours

when it is coldest outside.

200W * 1kW/1000W * $.11/kW-hr * 12hr/day = 0.26cents/day

*--> $/month *
*--> $8/Winter (6-months) *
Toby

Posted by *zoe_lithoi* on December 25, 2014, 5:53 pm

Greetings,

I took some temperature readings with a usb-type data logger for 2 days. on

e day had some 200Watt grow lights on, while the other did not. The 2 logge

rs, unfortunately were not very accurate because to start with, I had them

both inside a room next to each other, and one read 80degF while the other

read 82degF. I put one outside, and the other inside the greenhouse. I'm pa

sting the spreadsheet data here, and am not sure how it will appear when it

's processed by Google.

No Lights 200W Lights Notes

Tmp-I Tmp-O Tmp-I Tmp-O

Date Time Inside Outside Inside Outside

12/22/14 1616 80 82 Both Temp Probes

In House

12/22/14 1816 63

12/23/14 0 57 56

12/23/14 700 52 53 low Tmp-I & Tmp-O

Equalization: No Heat

Flow into or out of

Greenhouse

12/23/14 830 52 55

12/23/14 1306 82 High Tmp-O

Heat into Ground

12/23/14 1420 62 69 High Tmp-I

12/23/14 1545 62 64

12/24/14 0 50 35

12/24/14 300 30

12/24/14 500 43 30

12/24/14 545 43 30

I estimate the 'ground temperature' equals 53degF by noting that with the l

ights off on 12/23/14 for a period around 700 (7am), the outside temperatu

re and inside temperature were about equal. I call this equalization. There

was no heat flowing into the greenhouse from the outside, and there was no

heat flowing into or out of the greenhouse through the ground. This was an

other way to confirm my estimate in the previous posting on this thread whe

re I said the ground temperature about 4inches deep was about 50degF. IT's

not quite that simple. The temperatures 7 hours earlier at 0am on 12/23/14

show heat flowing from the greenhouse to the outside. This heat is being su

pplied by the ground. So what has happenned is that the ground temperature

had heated up (charged up) prior to that, and now this thermal capacitor wa

s discharging. The ground temperature had to have been greater than the gre

enhouse temp (57). What this tells me is that the ground temperature cycles

on that day from about 53 to 58F.

Let's make a better estimate of the overall thermal resistance of the Green

house by looking at the temperatures around 1420 to 1545 on 12/23/14. The g

reenhouse temperature, Trm, was 62F, and the outside air temperature was ab

out 65 to 66F (taking into account the 2deg temperature error mentioned abo

ve. In the last posting, I estimated that it had an R10 "R-Value" over a 27

3sqft surface area (walls and ceiling). Lets call this Rgv

Hrm = heat entering the greenhouse room of Temperature, Trm, from the ou

tside air of temperature To, thru the 273sqft of Rgv walls and ceiling

Hrm = (To - Trm)degF*273sqft / Rgv hr-sqft-degF/Btu]

Hrm = (To - Trm)*273/Rgv Btu/hr

Hgnd = ground heat entering the greenhouse room of Temperature, Trm, thr

u the 50sqft of R0.33 dirt with temperature Tg

Hgnd = (Tg - Trm)*50sqft / [0.33 hr-sqft-F/Btu]

Hgnd = (Tg - Trm)*150 Btu/hr

If the room gets new air each hour equivalent to it's volume, then the air-

exchange heat loss for the amount of heat the air in the 400cuft (8'*7'*7')

room absorbs to go from To degF to Trm is:

Hair = (To - Trm)degF * 1/55 Btu/F /cuft * 400cuft

Hair = (To - Trm)* 5 Btu/hr

And lastly, there is another source of heat flow radiative in nature, Hrad,

which for now we will assume is 0.

Kierkoff's Current (Heat) flow equation is:

Hrm + Hgnd + Hair + Hrad = 0

(To - Trm)*273/Rgv + (Tg - Trm)*150 + (To - Trm)*5 + 0 = 0

(To - Trm)*(273/Rgv + 5) + (Tg - Trm)*150 = 0

Now let's look at the data at 1420 to 1545 on 12/23/14 as stipulated:

Trm = 62F

To = 66F (The temperature range wa sfrom 69 to 64, but remember that this

temperature probe recorded a 2degF higher temperature at the same location

and time as the other probe, so the temp range was really 67 to 62. AT 62,

it would be the same temperature as the other probe. So we will look at th

e 66F.)

Tg = 57F (in reality it could be anywhere between 55 to 58F, but since it

's at the hottest part of the day and still charging up, 57F is a reasonabl

e estimate IMO.)

(66 - 62)*(273/Rgv + 5) + (57 - 62)*150 = 0

(4)*(273/Rgv + 5) - (5)*150 = 0

(4)*(273/Rgv + 5) - (5)*150 = 0

1092/Rgv + 20 - 750 = 0

1092/Rgv = 730

Rgv = 1092/730 = 1.5

huh. I would have expected more....

I'll have to relook at this and look at the data better.... and look at the

radiative heat

Toby

On Sunday, November 30, 2014 9:28:27 AM UTC-8, zoe_lithoi wrote:

*> Straw-infilled-Pallet Winter Greenhouse. *

*> Greetings, *

*> *

*> My son and I are building a 80" x 80" x 8'(tall) 'winter' Greenhouse made *

of pallets screwed together and stuffed with straw for insulation (R10?).

It has plastic stapled to the inside which should prevent heat loss by con

vection. The Roof has masonite siding on it in case of rain. We will have 2

00 of grow lights which will also serve as the primary heat source. The gro

und will be either a heat source or a heat sink (not sure yet.....). The go

al is to keep the temperature above freezing so the seedlings don't die.

*> *

*> The surface area of the 4 walls, and ceiling would be: *

*> *

*> A = 4*7*8 + 7*7 = 273 sqft *

*> *

*> The heat from the growlights *

*> Hgl = 200W * 3.41 Btu/1Watt-hr = 682 Btu/hr *

*> *

*> Hgnd = ground heat will be called: *

*> For now, we will assume that heat from the growlites will enter the groun *

d.

*> *

*> Hrm = heat leaving the room of Temperature, Trm, thru the 273sqft of R *

10 walls and ceiling to the 20degF outside is:

*> *

*> Hrm = (Trm - 20)degF*273sqft / R10 hr-sqft-degF/Btu] = (Trm - 20)* 27 *

Btu/hr

*> *

*> If the room gets new air each hour equivalent to it's volume, then the ai *

r-exchange heat loss for the amount of heat the air in the 400cuft (8'*7'*7

') room absorbs to go from 20degF to Trm is:

*> *

*> Hair = (Trm - 20)degF * 1/55 Btu/F /cuft * 400cuft ~= (Trm - 20) * 5 *

Btu/hr

*> *

*> The heatflow equation then, is: *

*> *

*> Hgl = Hgnd + Hrm + Hair *

*> 682 = Hgnd + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> *

*> For now, let's assume the heat flow into or out of the ground is 0, i.e.: *

*> Hgnd = 0 *

*> *

*> 682 = (Trm - 20)* 27 + (Trm - 20) * 5 *

*> 682 = 33*Trm - 20* (27 + 5) *

*> 682 = 33*Trm - 660 *

*> 1342 = 33*Trm *

*> Trm = 1342/33 = 41degF *

*> *

*> If the outside temperature was 0degF, then *

*> Trm = 682/33 = 21degF *

*> --- daid seedlings *

*> *

*> So we need to look at the ground temperature. *

*> *

*> In the above calc's, Trm is between 20 and 40degF. The Ground temperature *

, for the southwest (NEvada, Utah, Arizona), 4inches deep (the approix dept

h heat can travel in the ground in 1 hour --- see the 'daycreek' thread in

this group), is about 50degF. So as long as the greenhouse temperature, Trm

, is below 50degF, then the ground is a heat source and supplies heat to th

e greenhouse.

*> *

*> ----------------------------- *

*> *

*> -SAND Heat capacity 2.5 BTU/(F-sqft-in) *

*> -SAND Resistance 0.083 hr-sqft-F/(BTU-in) *

*> *

*> From past calculations and real-world example (daycreek.com), ground heat *

travels about 4inches per hour, so:

*> *

*> -SAND Heat capacity 2.5 BTU/(F-sqft-in) * 4inch = 10 BTU/F-sqft *

*> -SAND Resistance 0.083 hr-sqft-F/(BTU-in) * 4inch = 0.33 hr-sqft-F/ *

Btu

*> *

*> The surface area of the ground is: *

*> 7' x 7' = ~50sqft *

*> *

*> Hgnd = (50degF - Trm)*50sqft / [0.33 hr-sqft-F/Btu] *

*> Hgnd = (50degF - Trm) * 16.5 Btu/hr *

*> *

*> ------------------- *

*> Now let's include the ground heat in the heatflow equation which again is *

:

*> *

*> Hgl = - Hgnd + Hrm + Hair *

*> 682 = -(50degF - Trm) * 16.5 + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> 682 = (+16.5+27+5)*Trm - 50*16.5 - 20* (27 + 5) *

*> 682 = 44*Trm - 825 - 660 *

*> 2167 = 44*Trm *

*> Trm = 2167/44 = 49degF *

*> *

*> Now, if the outside temperature is 0degF (instead of 20degF): *

*> 682 = (+16.5+27+5)*Trm - 50*16.5 - 0* (27 + 5) *

*> 682 = 44*Trm - 825 *

*> 1597 = 44*Trm *

*> Trm = 1507/44 = 34 *

*> *

*> If a 400Watt growlite were used, and it was 0degF *

*> Hgl = 1364Btu/hr *

*> Then: *

*> 1364 = 44*Trm - 825 *

*> 2189 = 44*Trm *

*> Trm = 2189/44 = 50degF *

*> *

*> If there were not any growlites, and it was 20degF outside, then: *

*> 0 = 44*Trm - 825 - 660 *

*> 1485 = 44*Trm *

*> Trm = 1485/44 = 34degF *

*> *

*> The lowest daily low temperature in Las Vegas Nv for the month of July is *

40degF

*> See: https://weatherspark.com/averages/31890/1/Las-Vegas-Nevada-United-St *

ates

*> *

*> Daytime temperatures are normally in the 50's and 60's. *

*> *

*> Using Outside temperature of 40degF, with a 200W growlight we get: *

*> *

*> 682 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> 682 = 44*Trm - 825 - 1320 *

*> 2827 = 44*Trm *

*> Trm = 2827/44 = 64degF *

*> *

*> *

*> Using Outside temperature of 40degF, without a 200W growlight we get: *

*> *

*> 0 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> 0 = 44*Trm - 825 - 1320 *

*> 2145 = 44*Trm *

*> Trm = 2145/44 = 49degF *

*> *

*> So, one might have a thermostat to power the growlights if the temperatur *

e dropped below 45degF.... AND Further, put the growlites on a timer to giv

e it 12 hours each day (so the plants can get light) during night-time hour

s when it is coldest outside.

*> *

*> 200W * 1kW/1000W * $.11/kW-hr * 12hr/day = 0.26cents/day *

*> --> $/month *

*> --> $8/Winter (6-months) *

*> *

*> Toby *

Posted by *zoe_lithoi* on December 25, 2014, 7:03 pm

Greetings,

So, I'm refining my calculations by taking account the heatflow thru the do

or which I had just reckoned as part of the straw-infill greenhouse.

The ~2'x7' plywood 'door'has an Rvalue of about R0.5 hence the heatflow thr

u the door

Hdr = (To-Trm)*14sqft/R0.5sqft-degF-hr/Btu

Hdr = (To-Trm)* 28 Btu/hr

The surface area of the walls and ceiling can now be reduced by this 14sqft

as well, from 273 to 259sqft:

Hrm = (To - Trm)*259/Rgv Btu/hr

Kierkoff's Current (Heat) flow equation is now :

Hrm + Hdr + Hgnd + Hair + Hrad = 0

(To - Trm)*259/Rgv + (To-Trm)* 28 + (Tg - Trm)*150 + (To - Trm)*5 + 0 =

0

(To - Trm)*(259/Rgv + 28 + 5) + (Tg - Trm)*150 = 0

(To - Trm)*(259/Rgv + 33) + (Tg - Trm)*150 = 0

Now let's look at the data, as in the previous posting at 1420 to 1545 on 1

2/23/14 as stipulated:

Trm = 62F

To = 66F

Tg = 57F

(66 - 62)*(259/Rgv + 33) + (57 - 62)*150 = 0

(4)*(259/Rgv + 33) - (5)*150 = 0

(4)*(259/Rgv + 33) - (5)*150 = 0

1092/Rgv + 132 - 750 = 0

1036/Rgv = 618

Rgv = 1036/618 = 1.7

It 'still' should be more.

If the ground temp is 58 instead of 57.

(4)*(259/Rgv + 33) - (4)*150 = 0

1092/Rgv + 132 - 600 = 0

1036/Rgv = 468

Rgv = 1036/468 = 2.2

Toby

On Thursday, December 25, 2014 9:53:43 AM UTC-8, zoe_lithoi wrote:

*> Greetings, *

*> *

*> I took some temperature readings with a usb-type data logger for 2 days. *

one day had some 200Watt grow lights on, while the other did not. The 2 log

gers, unfortunately were not very accurate because to start with, I had the

m both inside a room next to each other, and one read 80degF while the othe

r read 82degF. I put one outside, and the other inside the greenhouse. I'm

pasting the spreadsheet data here, and am not sure how it will appear when

it's processed by Google.

*> *

*> No Lights 200W Lights Notes *

*> Tmp-I Tmp-O Tmp-I Tmp-O *

*> Date Time Inside Outside Inside Outside *

*> 12/22/14 1616 80 82 Both Temp Probes *

*> In House *

*> 12/22/14 1816 63 *

*> 12/23/14 0 57 56 *

*> 12/23/14 700 52 53 low Tmp-I & Tmp-O *

*> Equalization: No Heat *

*> Flow into or out of *

*> Greenhouse *

*> 12/23/14 830 52 55 *

*> 12/23/14 1306 82 High Tmp-O *

*> Heat into Ground *

*> 12/23/14 1420 62 69 High Tmp-I *

*> 12/23/14 1545 62 64 *

*> 12/24/14 0 50 35 *

*> 12/24/14 300 30 *

*> 12/24/14 500 43 30 *

*> 12/24/14 545 43 30 *

*> *

*> I estimate the 'ground temperature' equals 53degF by noting that with the *

lights off on 12/23/14 for a period around 700 (7am), the outside tempera

ture and inside temperature were about equal. I call this equalization. The

re was no heat flowing into the greenhouse from the outside, and there was

no heat flowing into or out of the greenhouse through the ground. This was

another way to confirm my estimate in the previous posting on this thread w

here I said the ground temperature about 4inches deep was about 50degF. IT'

s not quite that simple. The temperatures 7 hours earlier at 0am on 12/23/1

4 show heat flowing from the greenhouse to the outside. This heat is being

supplied by the ground. So what has happenned is that the ground temperatur

e had heated up (charged up) prior to that, and now this thermal capacitor

was discharging. The ground temperature had to have been greater than the g

reenhouse temp (57). What this tells me is that the ground temperature cycl

es on that day from about 53 to 58F.

*> *

*> Let's make a better estimate of the overall thermal resistance of the Gre *

enhouse by looking at the temperatures around 1420 to 1545 on 12/23/14. The

greenhouse temperature, Trm, was 62F, and the outside air temperature was

about 65 to 66F (taking into account the 2deg temperature error mentioned a

bove. In the last posting, I estimated that it had an R10 "R-Value" over a

273sqft surface area (walls and ceiling). Lets call this Rgv

*> *

*> Hrm = heat entering the greenhouse room of Temperature, Trm, from the *

outside air of temperature To, thru the 273sqft of Rgv walls and ceiling

*> Hrm = (To - Trm)degF*273sqft / Rgv hr-sqft-degF/Btu] *

*> Hrm = (To - Trm)*273/Rgv Btu/hr *

*> *

*> Hgnd = ground heat entering the greenhouse room of Temperature, Trm, t *

hru the 50sqft of R0.33 dirt with temperature Tg

*> Hgnd = (Tg - Trm)*50sqft / [0.33 hr-sqft-F/Btu] *

*> Hgnd = (Tg - Trm)*150 Btu/hr *

*> *

*> If the room gets new air each hour equivalent to it's volume, then the ai *

r-exchange heat loss for the amount of heat the air in the 400cuft (8'*7'*7

') room absorbs to go from To degF to Trm is:

*> *

*> Hair = (To - Trm)degF * 1/55 Btu/F /cuft * 400cuft *

*> Hair = (To - Trm)* 5 Btu/hr *

*> *

*> And lastly, there is another source of heat flow radiative in nature, Hra *

d, which for now we will assume is 0.

*> *

*> Kierkoff's Current (Heat) flow equation is: *

*> Hrm + Hgnd + Hair + Hrad = 0 *

*> (To - Trm)*273/Rgv + (Tg - Trm)*150 + (To - Trm)*5 + 0 = 0 *

*> (To - Trm)*(273/Rgv + 5) + (Tg - Trm)*150 = 0 *

*> *

*> Now let's look at the data at 1420 to 1545 on 12/23/14 as stipulated: *

*> Trm = 62F *

*> To = 66F (The temperature range wa sfrom 69 to 64, but remember that th *

is temperature probe recorded a 2degF higher temperature at the same locati

on and time as the other probe, so the temp range was really 67 to 62. AT 6

2, it would be the same temperature as the other probe. So we will look at

the 66F.)

*> Tg = 57F (in reality it could be anywhere between 55 to 58F, but since *

it's at the hottest part of the day and still charging up, 57F is a reasona

ble estimate IMO.)

*> *

*> (66 - 62)*(273/Rgv + 5) + (57 - 62)*150 = 0 *

*> (4)*(273/Rgv + 5) - (5)*150 = 0 *

*> (4)*(273/Rgv + 5) - (5)*150 = 0 *

*> 1092/Rgv + 20 - 750 = 0 *

*> 1092/Rgv = 730 *

*> Rgv = 1092/730 = 1.5 *

*> *

*> huh. I would have expected more.... *

*> *

*> I'll have to relook at this and look at the data better.... and look at t *

he radiative heat

*> *

*> Toby *

*> *

*> On Sunday, November 30, 2014 9:28:27 AM UTC-8, zoe_lithoi wrote: *

*> > Straw-infilled-Pallet Winter Greenhouse. *

*> > Greetings, *

*> > *

*> > My son and I are building a 80" x 80" x 8'(tall) 'winter' Greenhouse ma *

de of pallets screwed together and stuffed with straw for insulation (R10?)

. It has plastic stapled to the inside which should prevent heat loss by c

onvection. The Roof has masonite siding on it in case of rain. We will have

200 of grow lights which will also serve as the primary heat source. The g

round will be either a heat source or a heat sink (not sure yet.....). The

goal is to keep the temperature above freezing so the seedlings don't die.

*> > *

*> > The surface area of the 4 walls, and ceiling would be: *

*> > *

*> > A = 4*7*8 + 7*7 = 273 sqft *

*> > *

*> > The heat from the growlights *

*> > Hgl = 200W * 3.41 Btu/1Watt-hr = 682 Btu/hr *

*> > *

*> > Hgnd = ground heat will be called: *

*> > For now, we will assume that heat from the growlites will enter the gro *

und.

*> > *

*> > Hrm = heat leaving the room of Temperature, Trm, thru the 273sqft of *

R10 walls and ceiling to the 20degF outside is:

*> > *

*> > Hrm = (Trm - 20)degF*273sqft / R10 hr-sqft-degF/Btu] = (Trm - 20)* *

27 Btu/hr

*> > *

*> > If the room gets new air each hour equivalent to it's volume, then the *

air-exchange heat loss for the amount of heat the air in the 400cuft (8'*7'

*7') room absorbs to go from 20degF to Trm is:

*> > *

*> > Hair = (Trm - 20)degF * 1/55 Btu/F /cuft * 400cuft ~= (Trm - 20) * *

5 Btu/hr

*> > *

*> > The heatflow equation then, is: *

*> > *

*> > Hgl = Hgnd + Hrm + Hair *

*> > 682 = Hgnd + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > *

*> > For now, let's assume the heat flow into or out of the ground is 0, i.e *

.:

*> > Hgnd = 0 *

*> > *

*> > 682 = (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > 682 = 33*Trm - 20* (27 + 5) *

*> > 682 = 33*Trm - 660 *

*> > 1342 = 33*Trm *

*> > Trm = 1342/33 = 41degF *

*> > *

*> > If the outside temperature was 0degF, then *

*> > Trm = 682/33 = 21degF *

*> > --- daid seedlings *

*> > *

*> > So we need to look at the ground temperature. *

*> > *

*> > In the above calc's, Trm is between 20 and 40degF. The Ground temperatu *

re, for the southwest (NEvada, Utah, Arizona), 4inches deep (the approix de

pth heat can travel in the ground in 1 hour --- see the 'daycreek' thread i

n this group), is about 50degF. So as long as the greenhouse temperature, T

rm, is below 50degF, then the ground is a heat source and supplies heat to

the greenhouse.

*> > *

*> > ----------------------------- *

*> > *

*> > -SAND Heat capacity 2.5 BTU/(F-sqft-in) *

*> > -SAND Resistance 0.083 hr-sqft-F/(BTU-in) *

*> > *

*> > From past calculations and real-world example (daycreek.com), ground he *

at travels about 4inches per hour, so:

*> > *

*> > -SAND Heat capacity 2.5 BTU/(F-sqft-in) * 4inch = 10 BTU/F-sqft *

*> > -SAND Resistance 0.083 hr-sqft-F/(BTU-in) * 4inch = 0.33 hr-sqft- *

F/Btu

*> > *

*> > The surface area of the ground is: *

*> > 7' x 7' = ~50sqft *

*> > *

*> > Hgnd = (50degF - Trm)*50sqft / [0.33 hr-sqft-F/Btu] *

*> > Hgnd = (50degF - Trm) * 16.5 Btu/hr *

*> > *

*> > ------------------- *

*> > Now let's include the ground heat in the heatflow equation which again *

is:

*> > *

*> > Hgl = - Hgnd + Hrm + Hair *

*> > 682 = -(50degF - Trm) * 16.5 + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > 682 = (+16.5+27+5)*Trm - 50*16.5 - 20* (27 + 5) *

*> > 682 = 44*Trm - 825 - 660 *

*> > 2167 = 44*Trm *

*> > Trm = 2167/44 = 49degF *

*> > *

*> > Now, if the outside temperature is 0degF (instead of 20degF): *

*> > 682 = (+16.5+27+5)*Trm - 50*16.5 - 0* (27 + 5) *

*> > 682 = 44*Trm - 825 *

*> > 1597 = 44*Trm *

*> > Trm = 1507/44 = 34 *

*> > *

*> > If a 400Watt growlite were used, and it was 0degF *

*> > Hgl = 1364Btu/hr *

*> > Then: *

*> > 1364 = 44*Trm - 825 *

*> > 2189 = 44*Trm *

*> > Trm = 2189/44 = 50degF *

*> > *

*> > If there were not any growlites, and it was 20degF outside, then: *

*> > 0 = 44*Trm - 825 - 660 *

*> > 1485 = 44*Trm *

*> > Trm = 1485/44 = 34degF *

*> > *

*> > The lowest daily low temperature in Las Vegas Nv for the month of July *

is 40degF

*> > See: https://weatherspark.com/averages/31890/1/Las-Vegas-Nevada-United- *

States

*> > *

*> > Daytime temperatures are normally in the 50's and 60's. *

*> > *

*> > Using Outside temperature of 40degF, with a 200W growlight we get: *

*> > *

*> > 682 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> > 682 = 44*Trm - 825 - 1320 *

*> > 2827 = 44*Trm *

*> > Trm = 2827/44 = 64degF *

*> > *

*> > *

*> > Using Outside temperature of 40degF, without a 200W growlight we get: *

*> > *

*> > 0 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> > 0 = 44*Trm - 825 - 1320 *

*> > 2145 = 44*Trm *

*> > Trm = 2145/44 = 49degF *

*> > *

*> > So, one might have a thermostat to power the growlights if the temperat *

ure dropped below 45degF.... AND Further, put the growlites on a timer to g

ive it 12 hours each day (so the plants can get light) during night-time ho

urs when it is coldest outside.

*> > *

*> > 200W * 1kW/1000W * $.11/kW-hr * 12hr/day = 0.26cents/day *

*> > --> $/month *

*> > --> $8/Winter (6-months) *

*> > *

*> > Toby *

Posted by *zoe_lithoi* on December 25, 2014, 7:23 pm

Greetings,

I am continuing to refine my calculations. This time by taking into account

the radiative heat flow.

The room Temperature, Trm is 62F. The surface temperature of the floor is p

erhaps, TflaF

Now, radiant heatflow is generally calculated with the temperatures

in degree Rankine, not Fehrenheit. To convert:

Trankine = Tfehrenheit + 460

The standard radiation function is defined as follows:

Qrad = S*E*F*A*(Trm^4 - Tfl^4)

where:

S = Stefan-Boltzmann Constant (SBC) = 0.119 x 10-10 BTU/Hr*in^2*R^4

Note: this is a constant, and R4 means Rankine (as opposed to

Fehrenheit) raised to the 4th power..

= 0.119 x 10^-10 BTU/Hr*in^2*R^4 * 144 in^2/1 ft^2

= 1.714 x 10^-9 Btu/Hr*ft^2*R^4

E = emissivity = 0.9 (according to:

http://ciks.cbt.nist.gov/bentz/nistir6551/node14.html )

F = geometric form factor = 1.0

A = area = 50 sqft (for the surface above the floor of the greenhouse

)

Qrad = radiant heat flow rate (Heat/Time)

Tfl = Temperature of the floor surface in Rankine

Trm = room temperature in Rankine

Now, radiant heatflow is generally calculated with the temperatures

in degree Rankine, not Fehrenheit. To convert:

Trankine = Tfehrenheit + 460

Qrad = S*E*F*A*( (Trm+460)^4 - (Tfl+460)^4)

----------------------------------

Trm = 62F = 522 Rankine (The solar cistern's slab surface temperature)

Tfl = 61F = 521 Rankine

-----------------------------------

Qrad = FA(Tssc^4 - Th^4)

= 1.714x10^-9 Btu/Hr*ft^2*R^4 * 0.9*1* 50ft^2 *((522)^4

-(521)^4)

= 1.714x10^-9 Btu/Hr*ft^2*R^4 * 0.9*1* 50ft^2 *(7.424 x10^10 -7.368

x10^10)

= 77.13 * 0.056 x10^10

= 4.3 Btu/hr

Kierkoff's Current (Heat) flow equation is now :

Hrm + Hdr + Hgnd + Hair + Hrad = 0

(To - Trm)*259/Rgv + (To-Trm)* 28 + (Tg - Trm)*150 + (To - Trm)*5 + 4 =

0

(To - Trm)*(259/Rgv + 28 + 5) + (Tg - Trm)*150 + 4 = 0

(To - Trm)*(259/Rgv + 33) + (Tg - Trm)*150 + 4 = 0

Now let's look at the data, as in the previous posting at 1420 to 1545 on 1

2/23/14 as stipulated:

Trm = 62F

To = 66F

Tg = 58F

(66 - 62)*(259/Rgv + 33) + (58 - 62)*150 + 4 = 0

(4)*(259/Rgv + 33) - (4)*150 + 4 = 0

(4)*(259/Rgv + 33) - (4)*150 + 4 = 0

1092/Rgv + 132 - 600 + 4 = 0

1036/Rgv = 464

Rgv = 1036/464 = 2.23

It 'still' should be more.

Toby

On Thursday, December 25, 2014 11:03:42 AM UTC-8, zoe_lithoi wrote:

*> Greetings, *

*> *

*> So, I'm refining my calculations by taking account the heatflow thru the *

door which I had just reckoned as part of the straw-infill greenhouse.

*> *

*> The ~2'x7' plywood 'door'has an Rvalue of about R0.5 hence the heatflow t *

hru the door

*> Hdr = (To-Trm)*14sqft/R0.5sqft-degF-hr/Btu *

*> Hdr = (To-Trm)* 28 Btu/hr *

*> *

*> The surface area of the walls and ceiling can now be reduced by this 14sq *

ft as well, from 273 to 259sqft:

*> Hrm = (To - Trm)*259/Rgv Btu/hr *

*> *

*> Kierkoff's Current (Heat) flow equation is now : *

*> Hrm + Hdr + Hgnd + Hair + Hrad = 0 *

*> (To - Trm)*259/Rgv + (To-Trm)* 28 + (Tg - Trm)*150 + (To - Trm)*5 + 0 *

= 0

*> (To - Trm)*(259/Rgv + 28 + 5) + (Tg - Trm)*150 = 0 *

*> (To - Trm)*(259/Rgv + 33) + (Tg - Trm)*150 = 0 *

*> *

*> Now let's look at the data, as in the previous posting at 1420 to 1545 on *

12/23/14 as stipulated:

*> Trm = 62F *

*> To = 66F *

*> Tg = 57F *

*> *

*> (66 - 62)*(259/Rgv + 33) + (57 - 62)*150 = 0 *

*> (4)*(259/Rgv + 33) - (5)*150 = 0 *

*> (4)*(259/Rgv + 33) - (5)*150 = 0 *

*> 1092/Rgv + 132 - 750 = 0 *

*> 1036/Rgv = 618 *

*> Rgv = 1036/618 = 1.7 *

*> *

*> It 'still' should be more. *

*> If the ground temp is 58 instead of 57. *

*> (4)*(259/Rgv + 33) - (4)*150 = 0 *

*> 1092/Rgv + 132 - 600 = 0 *

*> 1036/Rgv = 468 *

*> Rgv = 1036/468 = 2.2 *

*> *

*> *

*> Toby *

*> *

*> On Thursday, December 25, 2014 9:53:43 AM UTC-8, zoe_lithoi wrote: *

*> > Greetings, *

*> > *

*> > I took some temperature readings with a usb-type data logger for 2 days *

. one day had some 200Watt grow lights on, while the other did not. The 2 l

oggers, unfortunately were not very accurate because to start with, I had t

hem both inside a room next to each other, and one read 80degF while the ot

her read 82degF. I put one outside, and the other inside the greenhouse. I'

m pasting the spreadsheet data here, and am not sure how it will appear whe

n it's processed by Google.

*> > *

*> > No Lights 200W Lights Notes *

*> > Tmp-I Tmp-O Tmp-I Tmp-O *

*> > Date Time Inside Outside Inside Outside *

*> > 12/22/14 1616 80 82 Both Temp Probes *

*> > In House *

*> > 12/22/14 1816 63 *

*> > 12/23/14 0 57 56 *

*> > 12/23/14 700 52 53 low Tmp-I & Tmp-O *

*> > Equalization: No Heat *

*> > Flow into or out of *

*> > Greenhouse *

*> > 12/23/14 830 52 55 *

*> > 12/23/14 1306 82 High Tmp-O *

*> > Heat into Ground *

*> > 12/23/14 1420 62 69 High Tmp-I *

*> > 12/23/14 1545 62 64 *

*> > 12/24/14 0 50 35 *

*> > 12/24/14 300 30 *

*> > 12/24/14 500 43 30 *

*> > 12/24/14 545 43 30 *

*> > *

*> > I estimate the 'ground temperature' equals 53degF by noting that with t *

he lights off on 12/23/14 for a period around 700 (7am), the outside tempe

rature and inside temperature were about equal. I call this equalization. T

here was no heat flowing into the greenhouse from the outside, and there wa

s no heat flowing into or out of the greenhouse through the ground. This wa

s another way to confirm my estimate in the previous posting on this thread

where I said the ground temperature about 4inches deep was about 50degF. I

T's not quite that simple. The temperatures 7 hours earlier at 0am on 12/23

/14 show heat flowing from the greenhouse to the outside. This heat is bein

g supplied by the ground. So what has happenned is that the ground temperat

ure had heated up (charged up) prior to that, and now this thermal capacito

r was discharging. The ground temperature had to have been greater than the

greenhouse temp (57). What this tells me is that the ground temperature cy

cles on that day from about 53 to 58F.

*> > *

*> > Let's make a better estimate of the overall thermal resistance of the G *

reenhouse by looking at the temperatures around 1420 to 1545 on 12/23/14. T

he greenhouse temperature, Trm, was 62F, and the outside air temperature wa

s about 65 to 66F (taking into account the 2deg temperature error mentioned

above. In the last posting, I estimated that it had an R10 "R-Value" over

a 273sqft surface area (walls and ceiling). Lets call this Rgv

*> > *

*> > Hrm = heat entering the greenhouse room of Temperature, Trm, from th *

e outside air of temperature To, thru the 273sqft of Rgv walls and ceiling

*> > Hrm = (To - Trm)degF*273sqft / Rgv hr-sqft-degF/Btu] *

*> > Hrm = (To - Trm)*273/Rgv Btu/hr *

*> > *

*> > Hgnd = ground heat entering the greenhouse room of Temperature, Trm, *

thru the 50sqft of R0.33 dirt with temperature Tg

*> > Hgnd = (Tg - Trm)*50sqft / [0.33 hr-sqft-F/Btu] *

*> > Hgnd = (Tg - Trm)*150 Btu/hr *

*> > *

*> > If the room gets new air each hour equivalent to it's volume, then the *

air-exchange heat loss for the amount of heat the air in the 400cuft (8'*7'

*7') room absorbs to go from To degF to Trm is:

*> > *

*> > Hair = (To - Trm)degF * 1/55 Btu/F /cuft * 400cuft *

*> > Hair = (To - Trm)* 5 Btu/hr *

*> > *

*> > And lastly, there is another source of heat flow radiative in nature, H *

rad, which for now we will assume is 0.

*> > *

*> > Kierkoff's Current (Heat) flow equation is: *

*> > Hrm + Hgnd + Hair + Hrad = 0 *

*> > (To - Trm)*273/Rgv + (Tg - Trm)*150 + (To - Trm)*5 + 0 = 0 *

*> > (To - Trm)*(273/Rgv + 5) + (Tg - Trm)*150 = 0 *

*> > *

*> > Now let's look at the data at 1420 to 1545 on 12/23/14 as stipulated: *

*> > Trm = 62F *

*> > To = 66F (The temperature range wa sfrom 69 to 64, but remember that *

this temperature probe recorded a 2degF higher temperature at the same loca

tion and time as the other probe, so the temp range was really 67 to 62. AT

62, it would be the same temperature as the other probe. So we will look a

t the 66F.)

*> > Tg = 57F (in reality it could be anywhere between 55 to 58F, but sinc *

e it's at the hottest part of the day and still charging up, 57F is a reaso

nable estimate IMO.)

*> > *

*> > (66 - 62)*(273/Rgv + 5) + (57 - 62)*150 = 0 *

*> > (4)*(273/Rgv + 5) - (5)*150 = 0 *

*> > (4)*(273/Rgv + 5) - (5)*150 = 0 *

*> > 1092/Rgv + 20 - 750 = 0 *

*> > 1092/Rgv = 730 *

*> > Rgv = 1092/730 = 1.5 *

*> > *

*> > huh. I would have expected more.... *

*> > *

*> > I'll have to relook at this and look at the data better.... and look at *

the radiative heat

*> > *

*> > Toby *

*> > *

*> > On Sunday, November 30, 2014 9:28:27 AM UTC-8, zoe_lithoi wrote: *

*> > > Straw-infilled-Pallet Winter Greenhouse. *

*> > > Greetings, *

*> > > *

*> > > My son and I are building a 80" x 80" x 8'(tall) 'winter' Greenhouse *

made of pallets screwed together and stuffed with straw for insulation (R10

?). It has plastic stapled to the inside which should prevent heat loss by

convection. The Roof has masonite siding on it in case of rain. We will ha

ve 200 of grow lights which will also serve as the primary heat source. The

ground will be either a heat source or a heat sink (not sure yet.....). Th

e goal is to keep the temperature above freezing so the seedlings don't die

.

*> > > *

*> > > The surface area of the 4 walls, and ceiling would be: *

*> > > *

*> > > A = 4*7*8 + 7*7 = 273 sqft *

*> > > *

*> > > The heat from the growlights *

*> > > Hgl = 200W * 3.41 Btu/1Watt-hr = 682 Btu/hr *

*> > > *

*> > > Hgnd = ground heat will be called: *

*> > > For now, we will assume that heat from the growlites will enter the g *

round.

*> > > *

*> > > Hrm = heat leaving the room of Temperature, Trm, thru the 273sqft *

of R10 walls and ceiling to the 20degF outside is:

*> > > *

*> > > Hrm = (Trm - 20)degF*273sqft / R10 hr-sqft-degF/Btu] = (Trm - 20) *

* 27 Btu/hr

*> > > *

*> > > If the room gets new air each hour equivalent to it's volume, then th *

e air-exchange heat loss for the amount of heat the air in the 400cuft (8'*

7'*7') room absorbs to go from 20degF to Trm is:

*> > > *

*> > > Hair = (Trm - 20)degF * 1/55 Btu/F /cuft * 400cuft ~= (Trm - 20) *

* 5 Btu/hr

*> > > *

*> > > The heatflow equation then, is: *

*> > > *

*> > > Hgl = Hgnd + Hrm + Hair *

*> > > 682 = Hgnd + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > > *

*> > > For now, let's assume the heat flow into or out of the ground is 0, i *

.e.:

*> > > Hgnd = 0 *

*> > > *

*> > > 682 = (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > > 682 = 33*Trm - 20* (27 + 5) *

*> > > 682 = 33*Trm - 660 *

*> > > 1342 = 33*Trm *

*> > > Trm = 1342/33 = 41degF *

*> > > *

*> > > If the outside temperature was 0degF, then *

*> > > Trm = 682/33 = 21degF *

*> > > --- daid seedlings *

*> > > *

*> > > So we need to look at the ground temperature. *

*> > > *

*> > > In the above calc's, Trm is between 20 and 40degF. The Ground tempera *

ture, for the southwest (NEvada, Utah, Arizona), 4inches deep (the approix

depth heat can travel in the ground in 1 hour --- see the 'daycreek' thread

in this group), is about 50degF. So as long as the greenhouse temperature,

Trm, is below 50degF, then the ground is a heat source and supplies heat t

o the greenhouse.

*> > > *

*> > > ----------------------------- *

*> > > *

*> > > -SAND Heat capacity 2.5 BTU/(F-sqft-in) *

*> > > -SAND Resistance 0.083 hr-sqft-F/(BTU-in) *

*> > > *

*> > > From past calculations and real-world example (daycreek.com), ground *

heat travels about 4inches per hour, so:

*> > > *

*> > > -SAND Heat capacity 2.5 BTU/(F-sqft-in) * 4inch = 10 BTU/F-sqft *

*> > > -SAND Resistance 0.083 hr-sqft-F/(BTU-in) * 4inch = 0.33 hr-sqf *

t-F/Btu

*> > > *

*> > > The surface area of the ground is: *

*> > > 7' x 7' = ~50sqft *

*> > > *

*> > > Hgnd = (50degF - Trm)*50sqft / [0.33 hr-sqft-F/Btu] *

*> > > Hgnd = (50degF - Trm) * 16.5 Btu/hr *

*> > > *

*> > > ------------------- *

*> > > Now let's include the ground heat in the heatflow equation which agai *

n is:

*> > > *

*> > > Hgl = - Hgnd + Hrm + Hair *

*> > > 682 = -(50degF - Trm) * 16.5 + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > > 682 = (+16.5+27+5)*Trm - 50*16.5 - 20* (27 + 5) *

*> > > 682 = 44*Trm - 825 - 660 *

*> > > 2167 = 44*Trm *

*> > > Trm = 2167/44 = 49degF *

*> > > *

*> > > Now, if the outside temperature is 0degF (instead of 20degF): *

*> > > 682 = (+16.5+27+5)*Trm - 50*16.5 - 0* (27 + 5) *

*> > > 682 = 44*Trm - 825 *

*> > > 1597 = 44*Trm *

*> > > Trm = 1507/44 = 34 *

*> > > *

*> > > If a 400Watt growlite were used, and it was 0degF *

*> > > Hgl = 1364Btu/hr *

*> > > Then: *

*> > > 1364 = 44*Trm - 825 *

*> > > 2189 = 44*Trm *

*> > > Trm = 2189/44 = 50degF *

*> > > *

*> > > If there were not any growlites, and it was 20degF outside, then: *

*> > > 0 = 44*Trm - 825 - 660 *

*> > > 1485 = 44*Trm *

*> > > Trm = 1485/44 = 34degF *

*> > > *

*> > > The lowest daily low temperature in Las Vegas Nv for the month of Jul *

y is 40degF

*> > > See: https://weatherspark.com/averages/31890/1/Las-Vegas-Nevada-Unite *

d-States

*> > > *

*> > > Daytime temperatures are normally in the 50's and 60's. *

*> > > *

*> > > Using Outside temperature of 40degF, with a 200W growlight we get: *

*> > > *

*> > > 682 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> > > 682 = 44*Trm - 825 - 1320 *

*> > > 2827 = 44*Trm *

*> > > Trm = 2827/44 = 64degF *

*> > > *

*> > > *

*> > > Using Outside temperature of 40degF, without a 200W growlight we get: *

*> > > *

*> > > 0 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> > > 0 = 44*Trm - 825 - 1320 *

*> > > 2145 = 44*Trm *

*> > > Trm = 2145/44 = 49degF *

*> > > *

*> > > So, one might have a thermostat to power the growlights if the temper *

ature dropped below 45degF.... AND Further, put the growlites on a timer to

give it 12 hours each day (so the plants can get light) during night-time

hours when it is coldest outside.

*> > > *

*> > > 200W * 1kW/1000W * $.11/kW-hr * 12hr/day = 0.26cents/day *

*> > > --> $/month *

*> > > --> $8/Winter (6-months) *

*> > > *

*> > > Toby *

Posted by *zoe_lithoi* on December 25, 2014, 7:51 pm

Greetings,

Something is not right.

I'm looking again at 2 things.

1. Rechecking the thermal resistance in the ground. We are looking at BTU p

er hour. Heat travels about 4" through the ground in 1 hour. (see the appe

ndix after my signature).

2. There is what is called a 'warm-still' air resistance in series with the

ground. It is small, and normally does not need to be taken into acount.

R0.67 sqft-hr-F/Btu for the warm air film

-----------------------------------

In 1 hour, the heat is supplied to the air by the 4" of dirt.

Dirt has an Rvalue of R0.083/inch

R0.083/inch * 4 = R0.33 sqft-hr-F/Btu for 4 inches of dirt

plus

R0.67 sqft-hr-F/Btu for the warm air film

= R1 sqft-hr-F/Btu

This is 3 times greater than my earlier value I used which was R0.33. So re

calculating the heat through the floor:

Hgnd = ground heat entering the greenhouse room of Temperature, Trm, thr

u the 50sqft of R1 dirt with temperature Tg

Hgnd = (Tg - Trm)*50sqft / [R1 hr-sqft-F/Btu]

Hgnd = (Tg - Trm)*50 Btu/hr

Kierkoff's Current (Heat) flow equation is now :

Hrm + Hdr + Hgnd + Hair + Hrad = 0

(To - Trm)*259/Rgv + (To-Trm)* 28 + (Tg - Trm)*50 + (To - Trm)*5 + 4 =

0

(To - Trm)*(259/Rgv + 28 + 5) + (Tg - Trm)*50 + 4 = 0

(To - Trm)*(259/Rgv + 33) + (Tg - Trm)*50 + 4 = 0

Now let's look at the data, as in the previous posting at 1420 to 1545 on 1

2/23/14 as stipulated:

Trm = 62F

To = 66F

Tg = 58F

(66 - 62)*(259/Rgv + 33) + (58 - 62)*50 + 4 = 0

(4)*(259/Rgv + 33) - (4)*50 + 4 = 0

1092/Rgv + 132 - 200 + 4 = 0

1036/Rgv = 64

Rgv = 1036/64 = 16.2

That is much more realistic!!!...

My original estimation was R10.... Maybe 16.2 is too large.

Let's go back to the earlier posting which used Tg as 57.

(66 - 62)*(259/Rgv + 33) + (57 - 62)*50 + 4 = 0

(4)*(259/Rgv + 33) - (5)*50 + 4 = 0

1092/Rgv + 132 - 250 + 4 = 0

1036/Rgv = 114

Rgv = 1036/114 = R9

This seems the best fit.

Let's look at even more data.

Toby

Toby

Appendix: Heat travels about 4inches into the ground in 1 hour.

Let's look at the depth, D, below 1 sqft of slab surface, As, heat

will travel in 1 hr, t:

t = time = 1hr

As = 1 sqft

tr = thermal resistivity = 1.7 hr*ft*F/Btu

(fig 11-1 of my earth-coupled heat transfer book)

Cv = 30 Btu/F/cuft

td = thermal diffusivity = 1/tr*C

-*-*-*-*-*-*-*-*-*

C = 30 Btu/F/cuft * D*1sqft = 30D Btu/F

td = 1/[(1.7 hr*ft*F/Btu)*(30D Btu/F)] = 1/51D sqft/hr

D = (1/51D sqft/hr)/(D ft) * 1 hr

D = 1/[51*D^2]

D^3 = 1/51 = 0.31 ft

D = (1/51)^(1/3) = 0.307' = 3.7"

On Thursday, December 25, 2014 11:23:10 AM UTC-8, zoe_lithoi wrote:

*> Greetings, *

*> *

*> I am continuing to refine my calculations. This time by taking into accou *

nt the radiative heat flow.

*> *

*> The room Temperature, Trm is 62F. The surface temperature of the floor is *

perhaps, TflaF

*> *

*> Now, radiant heatflow is generally calculated with the temperatures *

*> in degree Rankine, not Fehrenheit. To convert: *

*> *

*> Trankine = Tfehrenheit + 460 *

*> *

*> The standard radiation function is defined as follows: *

*> Qrad = S*E*F*A*(Trm^4 - Tfl^4) *

*> where: *

*> S = Stefan-Boltzmann Constant (SBC) = 0.119 x 10-10 BTU/Hr*in^2*R^4 *

*> Note: this is a constant, and R4 means Rankine (as opposed to *

*> Fehrenheit) raised to the 4th power.. *

*> = 0.119 x 10^-10 BTU/Hr*in^2*R^4 * 144 in^2/1 ft^2 *

*> = 1.714 x 10^-9 Btu/Hr*ft^2*R^4 *

*> E = emissivity = 0.9 (according to: *

*> http://ciks.cbt.nist.gov/bentz/nistir6551/node14.html ) *

*> F = geometric form factor = 1.0 *

*> A = area = 50 sqft (for the surface above the floor of the greenhou *

se)

*> Qrad = radiant heat flow rate (Heat/Time) *

*> Tfl = Temperature of the floor surface in Rankine *

*> Trm = room temperature in Rankine *

*> *

*> Now, radiant heatflow is generally calculated with the temperatures *

*> in degree Rankine, not Fehrenheit. To convert: *

*> *

*> Trankine = Tfehrenheit + 460 *

*> *

*> Qrad = S*E*F*A*( (Trm+460)^4 - (Tfl+460)^4) *

*> *

*> ---------------------------------- *

*> Trm = 62F = 522 Rankine (The solar cistern's slab surface temperature *

)

*> Tfl = 61F = 521 Rankine *

*> ----------------------------------- *

*> *

*> Qrad = FA(Tssc^4 - Th^4) *

*> = 1.714x10^-9 Btu/Hr*ft^2*R^4 * 0.9*1* 50ft^2 *((522)^4 *

*> -(521)^4) *

*> = 1.714x10^-9 Btu/Hr*ft^2*R^4 * 0.9*1* 50ft^2 *(7.424 x10^10 -7.368 *

*> x10^10) *

*> = 77.13 * 0.056 x10^10 *

*> = 4.3 Btu/hr *

*> *

*> Kierkoff's Current (Heat) flow equation is now : *

*> Hrm + Hdr + Hgnd + Hair + Hrad = 0 *

*> (To - Trm)*259/Rgv + (To-Trm)* 28 + (Tg - Trm)*150 + (To - Trm)*5 + 4 *

= 0

*> (To - Trm)*(259/Rgv + 28 + 5) + (Tg - Trm)*150 + 4 = 0 *

*> (To - Trm)*(259/Rgv + 33) + (Tg - Trm)*150 + 4 = 0 *

*> *

*> Now let's look at the data, as in the previous posting at 1420 to 1545 on *

12/23/14 as stipulated:

*> Trm = 62F *

*> To = 66F *

*> Tg = 58F *

*> *

*> (66 - 62)*(259/Rgv + 33) + (58 - 62)*150 + 4 = 0 *

*> (4)*(259/Rgv + 33) - (4)*150 + 4 = 0 *

*> (4)*(259/Rgv + 33) - (4)*150 + 4 = 0 *

*> 1092/Rgv + 132 - 600 + 4 = 0 *

*> 1036/Rgv = 464 *

*> Rgv = 1036/464 = 2.23 *

*> *

*> It 'still' should be more. *

*> *

*> Toby *

*> *

*> On Thursday, December 25, 2014 11:03:42 AM UTC-8, zoe_lithoi wrote: *

*> > Greetings, *

*> > *

*> > So, I'm refining my calculations by taking account the heatflow thru th *

e door which I had just reckoned as part of the straw-infill greenhouse.

*> > *

*> > The ~2'x7' plywood 'door'has an Rvalue of about R0.5 hence the heatflow *

thru the door

*> > Hdr = (To-Trm)*14sqft/R0.5sqft-degF-hr/Btu *

*> > Hdr = (To-Trm)* 28 Btu/hr *

*> > *

*> > The surface area of the walls and ceiling can now be reduced by this 14 *

sqft as well, from 273 to 259sqft:

*> > Hrm = (To - Trm)*259/Rgv Btu/hr *

*> > *

*> > Kierkoff's Current (Heat) flow equation is now : *

*> > Hrm + Hdr + Hgnd + Hair + Hrad = 0 *

*> > (To - Trm)*259/Rgv + (To-Trm)* 28 + (Tg - Trm)*150 + (To - Trm)*5 + 0 *

= 0

*> > (To - Trm)*(259/Rgv + 28 + 5) + (Tg - Trm)*150 = 0 *

*> > (To - Trm)*(259/Rgv + 33) + (Tg - Trm)*150 = 0 *

*> > *

*> > Now let's look at the data, as in the previous posting at 1420 to 1545 *

on 12/23/14 as stipulated:

*> > Trm = 62F *

*> > To = 66F *

*> > Tg = 57F *

*> > *

*> > (66 - 62)*(259/Rgv + 33) + (57 - 62)*150 = 0 *

*> > (4)*(259/Rgv + 33) - (5)*150 = 0 *

*> > (4)*(259/Rgv + 33) - (5)*150 = 0 *

*> > 1092/Rgv + 132 - 750 = 0 *

*> > 1036/Rgv = 618 *

*> > Rgv = 1036/618 = 1.7 *

*> > *

*> > It 'still' should be more. *

*> > If the ground temp is 58 instead of 57. *

*> > (4)*(259/Rgv + 33) - (4)*150 = 0 *

*> > 1092/Rgv + 132 - 600 = 0 *

*> > 1036/Rgv = 468 *

*> > Rgv = 1036/468 = 2.2 *

*> > *

*> > *

*> > Toby *

*> > *

*> > On Thursday, December 25, 2014 9:53:43 AM UTC-8, zoe_lithoi wrote: *

*> > > Greetings, *

*> > > *

*> > > I took some temperature readings with a usb-type data logger for 2 da *

ys. one day had some 200Watt grow lights on, while the other did not. The 2

loggers, unfortunately were not very accurate because to start with, I had

them both inside a room next to each other, and one read 80degF while the

other read 82degF. I put one outside, and the other inside the greenhouse.

I'm pasting the spreadsheet data here, and am not sure how it will appear w

hen it's processed by Google.

*> > > *

*> > > No Lights 200W Lights Notes *

*> > > Tmp-I Tmp-O Tmp-I Tmp-O *

*> > > Date Time Inside Outside Inside Outside *

*> > > 12/22/14 1616 80 82 Both Temp Probes *

*> > > In House *

*> > > 12/22/14 1816 63 *

*> > > 12/23/14 0 57 56 *

*> > > 12/23/14 700 52 53 low Tmp-I & Tmp-O *

*> > > Equalization: No Heat *

*> > > Flow into or out of *

*> > > Greenhouse *

*> > > 12/23/14 830 52 55 *

*> > > 12/23/14 1306 82 High Tmp-O *

*> > > Heat into Ground *

*> > > 12/23/14 1420 62 69 High Tmp-I *

*> > > 12/23/14 1545 62 64 *

*> > > 12/24/14 0 50 35 *

*> > > 12/24/14 300 30 *

*> > > 12/24/14 500 43 30 *

*> > > 12/24/14 545 43 30 *

*> > > *

*> > > I estimate the 'ground temperature' equals 53degF by noting that with *

the lights off on 12/23/14 for a period around 700 (7am), the outside tem

perature and inside temperature were about equal. I call this equalization.

There was no heat flowing into the greenhouse from the outside, and there

was no heat flowing into or out of the greenhouse through the ground. This

was another way to confirm my estimate in the previous posting on this thre

ad where I said the ground temperature about 4inches deep was about 50degF.

IT's not quite that simple. The temperatures 7 hours earlier at 0am on 12/

23/14 show heat flowing from the greenhouse to the outside. This heat is be

ing supplied by the ground. So what has happenned is that the ground temper

ature had heated up (charged up) prior to that, and now this thermal capaci

tor was discharging. The ground temperature had to have been greater than t

he greenhouse temp (57). What this tells me is that the ground temperature

cycles on that day from about 53 to 58F.

*> > > *

*> > > Let's make a better estimate of the overall thermal resistance of the *

Greenhouse by looking at the temperatures around 1420 to 1545 on 12/23/14.

The greenhouse temperature, Trm, was 62F, and the outside air temperature

was about 65 to 66F (taking into account the 2deg temperature error mention

ed above. In the last posting, I estimated that it had an R10 "R-Value" ove

r a 273sqft surface area (walls and ceiling). Lets call this Rgv

*> > > *

*> > > Hrm = heat entering the greenhouse room of Temperature, Trm, from *

the outside air of temperature To, thru the 273sqft of Rgv walls and ceilin

g

*> > > Hrm = (To - Trm)degF*273sqft / Rgv hr-sqft-degF/Btu] *

*> > > Hrm = (To - Trm)*273/Rgv Btu/hr *

*> > > *

*> > > Hgnd = ground heat entering the greenhouse room of Temperature, Tr *

m, thru the 50sqft of R0.33 dirt with temperature Tg

*> > > Hgnd = (Tg - Trm)*50sqft / [0.33 hr-sqft-F/Btu] *

*> > > Hgnd = (Tg - Trm)*150 Btu/hr *

*> > > *

*> > > If the room gets new air each hour equivalent to it's volume, then th *

e air-exchange heat loss for the amount of heat the air in the 400cuft (8'*

7'*7') room absorbs to go from To degF to Trm is:

*> > > *

*> > > Hair = (To - Trm)degF * 1/55 Btu/F /cuft * 400cuft *

*> > > Hair = (To - Trm)* 5 Btu/hr *

*> > > *

*> > > And lastly, there is another source of heat flow radiative in nature, *

Hrad, which for now we will assume is 0.

*> > > *

*> > > Kierkoff's Current (Heat) flow equation is: *

*> > > Hrm + Hgnd + Hair + Hrad = 0 *

*> > > (To - Trm)*273/Rgv + (Tg - Trm)*150 + (To - Trm)*5 + 0 = 0 *

*> > > (To - Trm)*(273/Rgv + 5) + (Tg - Trm)*150 = 0 *

*> > > *

*> > > Now let's look at the data at 1420 to 1545 on 12/23/14 as stipulated: *

*> > > Trm = 62F *

*> > > To = 66F (The temperature range wa sfrom 69 to 64, but remember tha *

t this temperature probe recorded a 2degF higher temperature at the same lo

cation and time as the other probe, so the temp range was really 67 to 62.

AT 62, it would be the same temperature as the other probe. So we will look

at the 66F.)

*> > > Tg = 57F (in reality it could be anywhere between 55 to 58F, but si *

nce it's at the hottest part of the day and still charging up, 57F is a rea

sonable estimate IMO.)

*> > > *

*> > > (66 - 62)*(273/Rgv + 5) + (57 - 62)*150 = 0 *

*> > > (4)*(273/Rgv + 5) - (5)*150 = 0 *

*> > > (4)*(273/Rgv + 5) - (5)*150 = 0 *

*> > > 1092/Rgv + 20 - 750 = 0 *

*> > > 1092/Rgv = 730 *

*> > > Rgv = 1092/730 = 1.5 *

*> > > *

*> > > huh. I would have expected more.... *

*> > > *

*> > > I'll have to relook at this and look at the data better.... and look *

at the radiative heat

*> > > *

*> > > Toby *

*> > > *

*> > > On Sunday, November 30, 2014 9:28:27 AM UTC-8, zoe_lithoi wrote: *

*> > > > Straw-infilled-Pallet Winter Greenhouse. *

*> > > > Greetings, *

*> > > > *

*> > > > My son and I are building a 80" x 80" x 8'(tall) 'winter' Greenhous *

e made of pallets screwed together and stuffed with straw for insulation (R

10?). It has plastic stapled to the inside which should prevent heat loss

by convection. The Roof has masonite siding on it in case of rain. We will

have 200 of grow lights which will also serve as the primary heat source. T

he ground will be either a heat source or a heat sink (not sure yet.....).

The goal is to keep the temperature above freezing so the seedlings don't d

ie.

*> > > > *

*> > > > The surface area of the 4 walls, and ceiling would be: *

*> > > > *

*> > > > A = 4*7*8 + 7*7 = 273 sqft *

*> > > > *

*> > > > The heat from the growlights *

*> > > > Hgl = 200W * 3.41 Btu/1Watt-hr = 682 Btu/hr *

*> > > > *

*> > > > Hgnd = ground heat will be called: *

*> > > > For now, we will assume that heat from the growlites will enter the *

ground.

*> > > > *

*> > > > Hrm = heat leaving the room of Temperature, Trm, thru the 273sqf *

t of R10 walls and ceiling to the 20degF outside is:

*> > > > *

*> > > > Hrm = (Trm - 20)degF*273sqft / R10 hr-sqft-degF/Btu] = (Trm - 2 *

0)* 27 Btu/hr

*> > > > *

*> > > > If the room gets new air each hour equivalent to it's volume, then *

the air-exchange heat loss for the amount of heat the air in the 400cuft (8

'*7'*7') room absorbs to go from 20degF to Trm is:

*> > > > *

*> > > > Hair = (Trm - 20)degF * 1/55 Btu/F /cuft * 400cuft ~= (Trm - 2 *

0) * 5 Btu/hr

*> > > > *

*> > > > The heatflow equation then, is: *

*> > > > *

*> > > > Hgl = Hgnd + Hrm + Hair *

*> > > > 682 = Hgnd + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > > > *

*> > > > For now, let's assume the heat flow into or out of the ground is 0, *

i.e.:

*> > > > Hgnd = 0 *

*> > > > *

*> > > > 682 = (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > > > 682 = 33*Trm - 20* (27 + 5) *

*> > > > 682 = 33*Trm - 660 *

*> > > > 1342 = 33*Trm *

*> > > > Trm = 1342/33 = 41degF *

*> > > > *

*> > > > If the outside temperature was 0degF, then *

*> > > > Trm = 682/33 = 21degF *

*> > > > --- daid seedlings *

*> > > > *

*> > > > So we need to look at the ground temperature. *

*> > > > *

*> > > > In the above calc's, Trm is between 20 and 40degF. The Ground tempe *

rature, for the southwest (NEvada, Utah, Arizona), 4inches deep (the approi

x depth heat can travel in the ground in 1 hour --- see the 'daycreek' thre

ad in this group), is about 50degF. So as long as the greenhouse temperatur

e, Trm, is below 50degF, then the ground is a heat source and supplies heat

to the greenhouse.

*> > > > *

*> > > > ----------------------------- *

*> > > > *

*> > > > -SAND Heat capacity 2.5 BTU/(F-sqft-in) *

*> > > > -SAND Resistance 0.083 hr-sqft-F/(BTU-in) *

*> > > > *

*> > > > From past calculations and real-world example (daycreek.com), groun *

d heat travels about 4inches per hour, so:

*> > > > *

*> > > > -SAND Heat capacity 2.5 BTU/(F-sqft-in) * 4inch = 10 BTU/F-sqft *

*> > > > -SAND Resistance 0.083 hr-sqft-F/(BTU-in) * 4inch = 0.33 hr-s *

qft-F/Btu

*> > > > *

*> > > > The surface area of the ground is: *

*> > > > 7' x 7' = ~50sqft *

*> > > > *

*> > > > Hgnd = (50degF - Trm)*50sqft / [0.33 hr-sqft-F/Btu] *

*> > > > Hgnd = (50degF - Trm) * 16.5 Btu/hr *

*> > > > *

*> > > > ------------------- *

*> > > > Now let's include the ground heat in the heatflow equation which ag *

ain is:

*> > > > *

*> > > > Hgl = - Hgnd + Hrm + Hair *

*> > > > 682 = -(50degF - Trm) * 16.5 + (Trm - 20)* 27 + (Trm - 20) * 5 *

*> > > > 682 = (+16.5+27+5)*Trm - 50*16.5 - 20* (27 + 5) *

*> > > > 682 = 44*Trm - 825 - 660 *

*> > > > 2167 = 44*Trm *

*> > > > Trm = 2167/44 = 49degF *

*> > > > *

*> > > > Now, if the outside temperature is 0degF (instead of 20degF): *

*> > > > 682 = (+16.5+27+5)*Trm - 50*16.5 - 0* (27 + 5) *

*> > > > 682 = 44*Trm - 825 *

*> > > > 1597 = 44*Trm *

*> > > > Trm = 1507/44 = 34 *

*> > > > *

*> > > > If a 400Watt growlite were used, and it was 0degF *

*> > > > Hgl = 1364Btu/hr *

*> > > > Then: *

*> > > > 1364 = 44*Trm - 825 *

*> > > > 2189 = 44*Trm *

*> > > > Trm = 2189/44 = 50degF *

*> > > > *

*> > > > If there were not any growlites, and it was 20degF outside, then: *

*> > > > 0 = 44*Trm - 825 - 660 *

*> > > > 1485 = 44*Trm *

*> > > > Trm = 1485/44 = 34degF *

*> > > > *

*> > > > The lowest daily low temperature in Las Vegas Nv for the month of J *

uly is 40degF

*> > > > See: https://weatherspark.com/averages/31890/1/Las-Vegas-Nevada-Uni *

ted-States

*> > > > *

*> > > > Daytime temperatures are normally in the 50's and 60's. *

*> > > > *

*> > > > Using Outside temperature of 40degF, with a 200W growlight we get: *

*> > > > *

*> > > > 682 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> > > > 682 = 44*Trm - 825 - 1320 *

*> > > > 2827 = 44*Trm *

*> > > > Trm = 2827/44 = 64degF *

*> > > > *

*> > > > *

*> > > > Using Outside temperature of 40degF, without a 200W growlight we ge *

t:

*> > > > *

*> > > > 0 = (+16.5+27+5)*Trm - 50*16.5 - 40* (27 + 5) *

*> > > > 0 = 44*Trm - 825 - 1320 *

*> > > > 2145 = 44*Trm *

*> > > > Trm = 2145/44 = 49degF *

*> > > > *

*> > > > So, one might have a thermostat to power the growlights if the temp *

erature dropped below 45degF.... AND Further, put the growlites on a timer

to give it 12 hours each day (so the plants can get light) during night-tim

e hours when it is coldest outside.

*> > > > *

*> > > > 200W * 1kW/1000W * $.11/kW-hr * 12hr/day = 0.26cents/day *

*> > > > --> $/month *

*> > > > --> $8/Winter (6-months) *

*> > > > *

*> > > > Toby *

> Straw-infilled-Pallet Winter Greenhouse.> Greetings,>> My son and I are building a 80" x 80" x 8'(tall) 'winter' Greenhouse made