Abraxas FAQs

MarketManager does correctly size a water-air heat pump based upon your inputs for zone loads and COP. MarketManager will not size the ground loop. Instead it assumes that a ground loop with a sufficient heat source exists. However, there is an error in the hourly simulation of earth-coupled heat pumps with an easy "workaround", as explained below.

Here's how the simulation is supposed to work: as noted above, the ground loop is assumed to always be fully charged. So if you make sure the water-air heat pump is at or greater than the default capacity, it will be able to meet the annual heating load for the zone.

But because of a programming error, MarketManager loses track of the heat source for the ground loop (the earth) even though the loop is still assumed to be fully charged. So the water-air heat pump has no problem meeting the zone heating load (assuming it is sized correctly), but MarketManager doesn't know the source of the heat for the loop. As a result, it reports "unmet heating hours". These are really unmet hours for the ground loop, not the zone. So increasing the size of the water-air heat pump makes no difference, it is already of sufficient capacity to extract heat from the loop.

There are two workarounds you can follow:

1. Do nothing. If you do not need a backup boiler, don't add one in MarketManager. While you will get the annoying message that there are unmet heating hours, this is for the ground loop recharging only, not for the zone.
2. Add a "dummy" backup boiler. Size it large enough that the unmet hours disappear after simulation. Make sure that the fuel for the boiler is *free*, i.e. that it is not attached to a meter with an energy rate. Also make sure there is no auxiliary power used by the boiler. Zero out the pump in the boiler detail form. Also make sure this dummy boiler is set for only Increm/HP Loop in the detail form. If you have other boilers, that is fine, just make sure that they are not set for Increm/HP Loop in the detail form.

Whether you add a boiler or not, you will still get the same energy usage from your water air heat pump.

If you allow MarketManager to autosize your heatpump, you should meet the load. MarketManager sizes heatpumps according to the methods described in the ASHRAE manuals using design temperatures. If you look at diagnostics and look at on fraction for January, you will see that the heatpump is on 100% during the coldest hour of the month.

You may not require a backup heating source for in your area. Be aware, though, that MarketManager is sizing the heatpump only, and not the water loop. As long as ample heating energy arrives at the water air heatpump, the autosized heatpump should be large enough to move the heating energy in the water loop to the space.