I am building a new house in Manitoba (Canada). My calculated heating load is 124,211 BTUh. Cooling load is 58,117 Btuh. Winter design is to - 27 degrees F and summer to 86 degrees F. Estimated annual heating loads are 239 million Btu and 28.5 million Btu cooling. Heated area is about 8000 sq ft. The house will be well insulated (exterior foam, possibly spray foam interior). I have to go with vertical loops because of size of the lot. I can fit approximately 2000 feet in the front yard and 1000 feet in the back yard. Putting loops in the back yard is particularly challenging as I have to get permission from rivers and streams (the property is on a river) and access is a challenge. I am installing two masonry heaters which when fired will create 6500 to 10,000 btu each over 24 hours. I obviously have to be there to fire them. 2/3 of the heated space will be in-floor concrete radiant. A high velocity ducting system will be heating the remainder and cooling the whole building in the summer. I have been given the options of two waterfurnace 4 tonne units with 2200 ft of loop (ie. all in the front yard), One 4 tonne unit and a 6 ton unit with 2700 ft of loop or two 6 tonne units and 3000 ft of loop. The latter two options obviously require putting loops in the back yard and the associated grief. Incremental costs for each step up are approximately $5,000. All three systems would have a 20 KW Thermolec electric boiler as back-up. Domestic hot water will be provided by one heat pump in each system. Any thoughts as to what option I should choose would be greatly appreciated.

I'm not sure I'd go high velocity in new construction - There are very few (?one?) player in high velocity. New construction offers design choices which should allow use of standard ducts. High velocity comes with compromises in cost, choices and reduced efficiency. getting it right (avoiding noise and uncomfortable drafts) is tricky.

Given the difficulty of back yard loops, and the masonry heater backup plan I'd consider installing no more geo tonnage than the front yard can support.

Consider also insulation and glass options that would reduce the heating load of the structure. If you could get the heat load down to 100k the two 4 tonne WFs could meet the load most of the time.

I see 8 tons as a good fit. Winnipeg shows -33*f as a design low so it should be ball park.
You need to ask what % of the load each system intends to handle with geo.
I second the comments about high velocity systems.....they are a compromise for a difficult situation not a designed in feature (IMHO).
good luck,
Joe

> Consider also insulation and glass options that would reduce the heating load of the structure.

I agree - plus look very carefully at air infiltration/sealing. Take a look at some PassiveHouse designs for ideas.

Question.  Is it possible to use the river as a water source? Unless it completely freezes in the winter, which is doubtful, since you said it was a river and not a creek or stream, could you use it as the source for an open loop system?

8000 Sq. Ft.? And they said American's Had McMansion fever. 

   

Hi. I'm a newby here and I've been searching this site to find out what a ' high velocity system" is. After googling around a bit, I get the feeling that it is a proprietary system of a particular manufacturer. It looks like Canada and the US each have a manufacturer claiming this and they are two distinctly different systems. Am I correct?

There are two high velocity duct systems that I am aware of:

Unico: http://unicosystem.com/
Spacepak: http://www.spacepak.com/

I did receive estimates for these systems because I have an old home and needed a retrofit. What both of these products are is a 2 inch flexible circular duct which is insulated. It fits between walls and the output is a small 2 inch circular hole.

I ended up not installing this type of system.

Note that I live on a river in Ontario. Other than bureaucratic BS hoops there was no problem getting the OK to put my loop in the river. It works fine. Be sure to put LOTS of weight on it though if you've got current. My 1st spring the current picked up the loop and wrapped it all over the place. My loop (2200' for a 5 1/2 ton Next Energy / ClimateMaster)is now wrapped twice with cable and has a cement bag on it every 50'.

Since the average ground temperature in most of Manitoba is 43 degrees Fahrenheit, the design must consider that the entering water temperature could be as low as 25 degrees Fahrenheit towards the end of the heating season. A ground source heat pump with a northern climate design will produce approximately 10,000 btu/h of heat for every nominal ton of cooling capacity. Since 90% of the time you only need 60% of the energy, two stage equipment makes a lot of sense. GeoComfort makes a 12 ton single phase 2 stage hydronic heat pump that would fit the bill nicely. Their unit has two totally separate refrigerant circuits and separate controls systems meaning that there is now some redundancy in the system. The forced air portion of the system can be high velocity such as Unico, using hot or chilled water produced by the geothermal system.
High velocity systems have an advantage over conventional when coupled with geothermal because of their very large water coil and low cfm, discharge air temperature will be considerably higher. Unico's slot diffusers have an NC rating of 25, very respectable. Any additional heat requirement could be met by adding electric resistance to the air handlers.

The most important thing is to get the right mechanical contractor for the job. Ask for references that are at least two years old.

Thank you to everyone who has weighed in on the issue. It is gratifying to see that there is some consensus with going with the smaller units. Hopefully I can get away with it as I am installing triple pane double hit low e argon fibreglass windows http://www.accuratedorwin.com/ and rigid foam exterior and spray foam interior. My contractor is encouraging me to go with the hi-velocity system http://www.hi-velocity.com/ . He has done a couple of homes with it and has been happy. Considering the controversy in this thread I will get a quote done for standard ducting. I unfortunately cannot put loops into the river. I looked into it and it isn't feasible. The riverbank is clay and prone to significant restructuring each spring as massive ice jams move down the river. I am pretty confident with my geothermal installer. Manitoba apparently has one of the highest densities of geothermal installations in North America. That is one of the benefits of living on the bottom of glacial lake Agassiz.

Well we certainly know what you distribute ST.
I agree with everything you said (in the last 2 sentences).
j