It's all Plain to Sea

[randy]

Finally finsihed construction and installation of the last of three air distribution boxes. Now circular openings for intake and exhaust need to be cut into the tops of the boxes and fans and air tube installed. I am waiting for the electrician to return to complete all the wiring including the fans and dampers.

[randy]

Recall that this greenhouse is constructed over springs that are actively outgassing CO2. A drainage system is intalled beneath the greenhouse that serves to provide drainage and capture the CO2. Access to the drainage system is provided by two standpipes at opposite corners of the greenhouse. A fan placed at one standpipe will draw air through the drainage system extracting the CO2 as required.

Any greenhouse full of growing plants, conventional or SHCS, requires input of CO2 at some point to allow continued photosynthesis. This can easily be accomplished by standard ventilation replacing internal greenhouse air with fresh outside air, generating CO2 or introducing CO2 from a manufactured source. The problem with standard ventilation is the SHCS is bypassed. The problem with generating CO2 with burners is the heat that is generated (not convenient in July). Manufactered sources have additional costs. The drainage system installed beneath my greenhouse will allow the introduction of CO2 without the previously mentioned problems. I should be able to achieve a fully closed system.

The last CO2 measurements that I took were last summer just after installation of the dranaige system. At that point the greenhouse had not been installed and the two standpipes were exposed to ambient air. I took the measurements at the two standpipe openings and the levels were in the 5000 ppm range. Sinse then the greenhouse and headhouse have been intalled, connected and made weathertight. Electric service and all fixtures have been installed in the headhouse and I am now ready to begin seeding. Electric service and growing systems are not yet complete in the greenhouse (including fans, etc. for the SHCS). I took three CO2 readings yesterday as follows: Basement of the headhouse 3.5 %; seedling bench in headouse 1.4% and middle of the greenhouse 1%. Note these readings!...1% is 10,000 ppm! At this point I have problem, these readings are not only too high for plants but present a concern to human safety. Up to this point the two standpipes in the greenhouse have remained open. The headhouse is at the lower end of the project and CO2 is heavier than air which would account for higher CO2 levels in the headhouse and the basement of the headhouse. I will seal the drainage system standpipes and continue to monitor the CO2 levels.

[mrhobbithhnet]

Looks like there won't be a lack of CO2 after all.

You never know, there might be a credit available to someone capping and using up natural CO2 sources. Wouldn't that be special.

Glad to hear you are setting up for your first plantings - that's always exciting. I hope you meet your construction goals in time for a spring planting.
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[randy]

Electricians have been at work off and on. One more day to complete their work when they decide to come back. Yesterday I completed installation and testing of the first of three SHCS fans. Everything seems to be working just fine. The fan is set up to pull suction through the SHCS. I will complete installation and testing of the remaining two fans today. I have ordered a Sentinel CHHC-1 environmental controler and expect delivery next week.



200 bell pepper were seeded in 2"x2"x1.5" Grogan rockwool cubes last Sunday. These will be germinating this week. 500 tomato will be seeded in about two weeks with cucumber, lettuce and mesclun to follow. I am looking to have produce ready about the end of May.

[randy]

SHCS, fans and the intake duct is in place. I have yet to install the poly duct on the exaust side and the Sentinel CHHC-1 controler. In addition, a misting system will be installed with 51, 1.02 gph emitters above the plant canopy level.

[mrhobbithhnet]

Things are looking up! How's the temps doing as far as the SHCS sucking up heat? Any luck keeping it from overheating too much? It'll need the misters soon... I hope you can get the Sentinel set up with SHCS input and output temps and RH readings, that'll give you perfect readings on the instantaneous heat exchange rate. Hope you get your plant in soon... glad to hear you are expecting growing climate in there so soon in the year.
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[randy]

Half the greenhouse floor is in place. This is a 6 oz black/white woven polyethylene fabric. Under the fabric is pex tubing imbedded in the sand. This will provide root zone hydronic heating.



The piping and nozzels are in place, overhead, for the misting system. Posts for the plant support system are in place where the floor has been installed.

[randy]

I have had difficulty keeping the CO2 down. The high levels of CO2 have damaged my seedlings. The solution is to use the very system designed to intercept and direct the CO2 into the greenhouse to direct it out. Photo below.



I do have the floor, plant support and most of the plumming complete. Next week the NFT system will be installed and I will finally be able to move plants into the greenhouse.

[randy]

Finishing installation and systems checks on the misting system and the nft system. Some minor bugs remain to be worked out but all is functioning. Weather forecast indicates several days of mostly cloudy conditions so tomorrow I will try to move seedlings into the greenhouse and set them up in the nft system.

Outside nightly lows remain well below freezing. Inside nightly lows drop into the high 30's with frost building up on the poly cover. As the morning sun hits the greenhouse this frost melts and rains down. The air exiting the SHCS drops to low of about 60. I will set up poly vent tubing to spread this air across the floor. This should provide temps near the floor somewhere between the SHCS exhaust temp and the greenhouse air temp. This will not optimum.

I have tested the mechanical fuctionality of the misting system. Other than some clogged nozzles everything works. The mist does lower the air temp and raise the humidity however, operation of the system also causes a rainstorm. I have yet to fully test the misting system's capability.

I hope that the moisture problem will be resolved by adequate drying time before sunset.

I have attached a couple of photos of the nft system.

[mrhobbithhnet]

Sounds like the mist condensing inside is a big issue...

I tend to think that it should be reserved for use only when there's enough solar gain to prevent dewpoint on inside surfaces during the day. If there was some way to monitor surface dewpoint on the inside of the cover, you could start and stop misting only when optimal for heat exchange. Maybe just a temperature enabled timer would work for now. Or maybe a temp and RH 'stat in series with the misting solenoid...

Hope you get the plants in. The greenhouse has been waiting so long... it'll be so great to see some green there.
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[randy]

How about some green, finally!



Check out the root growth. These tomato plants were well overdue for transplanting. They were too tall so they were inserted with the stem
laying down. This was nearly two weeks ago. The stems have turned up nicely and roots have emerged from the stem in the nft channel.



More on topic, I have been too busy putting all this together to closely monitor the performance on the greenhouse with the SHCS. I have however, decided the mid-day temps are too high even with the misting system operating. I have decided to install conventional ventilation. I think a fan installed high on one end with shutters high on the other end would operate mid-day to extract hot air from the peak of the greenhouse. I have been measuring temps at the peak in excess of 120 dF and seldom over 30 % rh, with misting system running. The intake for the SHCS is at the peak.The exhuast from the SHCS during these hours is about 80 dF and 85% rh. Even though the SHCS exhaust is distributed across the greenhouse at floor level with poly vent tube, the air temp rises rapidly above 100 dF. I have been trying to keep track of some temps and humidities and convert those to vapor pressure deficit(vpd). There are few times during the day when the vpd is in the optimal range. The tomatoes seem to be doing OK but I have no experience to indicate if their growth is reasonable. I am worried about heat stress and sufficient air movement. I am not sure if I should be worried about pathogens. I don't know how these environmental conditions will effect pollination and fruit development.

[mrhobbithhnet]

Nice! It's great to see some all the growth happening now.

It does look like you are have some issues with not enough heat being extracted. Normal, from what I've seen of conventional layouts, would be 90degF/90%RH in, 60/80 out this time of year. Those kinds of figures were usually with my lower recommendations for fan speed though...

You are on the right track though to be monitoring enough to generate some VPD data. Such low RH at high temp is curious to me... you can operate a swamp cooler efficiently at anything below 40%. I would never expect that you could be drying the air out that much with your recirc SHCS!?

For now, I'd be doing exactly what you are doing (taking advantage of fresh air for cooling) till you can get a bead on what direction to go with your SHCS and humidity control. As it is, it's going off it's cooling capacity curve way too early in the year.

I can't tell if it's your camera or the plants, but they look a little pale too. What do you think?
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